Troubleshooting atlas

A failed negative is evidence. Thin shadows, dense highlights, fog, streaks, uneven density, reticulation, stains, pinholes and drag marks each come from a limited set of causes, and each cause leaves a signature that can be read. This atlas is organised by what you see. Each entry describes the defect, lists the likely causes in order of how often they turn out to be the answer, explains the chemistry or physics that produces the appearance, gives the diagnostic questions that separate one cause from another, and states the corrective action and the prevention.

!There are no plates in this atlas yet, and here is why

A diagnostic atlas ought to show you the defect. This one does not, and it will not pretend otherwise. The course holds no photographs of a drying mark, a comet or a dichroic veil, and its own rules forbid describing an image it does not have or taking one from an arbitrary website.

On 5 September 2026 the course owner ruled that both atlases ship text-only now, and that plates are a later enhancement rather than a gate. The reasoning is that the diagnostic reasoning is the durable half. A photograph helps you recognise a drying mark; the sentence explaining what caused it is what teaches, and it is what lets you tell that mark from the three marks it resembles. Holding the whole reference back until somebody has spoiled, kept and photographed a hundred and forty-three sheets would have cost far more than it bought.

So every entry here is written from what the course has established in its own written parts, with a link back to the page that established it, and each carries a confirming test in place of a picture — something you can actually do that separates this defect from the ones it looks like. Where a signature is derived from the physics rather than observed, the entry says so in its own words. When the plates come, they drop into entries that were already built to hold them.

✦Tip

The habit the atlas teaches is to change one thing. A negative with three possible causes is diagnosed by an experiment that isolates one of them, not by changing developer, time and agitation at once and hoping. The experimental method taught in the developer laboratory part of the course is the same method used here.

Where the entries come from, and what is still missing

The register of everything this atlas owes is src/data/defects-planned.json, and npm run validate:atlases counts the written entries against it on every build, so the shortfall is a number rather than an impression.

The entries here were written in two passes, and each entry says on its face which it belongs to.

Most were lifted from the parts of the course that are already written — the laboratory and measurement faults from Part II and Part III, the coating defects from Part V, the camera, leak and exposure faults from Part VI, the development faults from Part IX, the fixing faults from Part XI, the washing and permanence faults from Part XII, and the curve, control-chart and instrument signatures from Parts XIII, XIV and XV. Several of those rows are assigned by the design to Part XXVIII, which was unwritten when they were lifted; each of those entries now names the Part XXVIII page that owns it and still says that it predates its owner, so that a later author can see exactly what was inherited and from where.

The rest were built from the course’s own reference corpus where the corpus could carry them: the chemical encyclopaedia, the formulary, the safety library and the sourced technical literature those were written from. That is how the printing, toning and alternative-process faults come to be here independently of the teaching sequence in Parts XVI to XXV — the causes of a mottled toned print, a bleached cyanotype or a stained platinotype are established chemistry that the course already holds, and an entry that reports it with its sources is not an entry invented from general knowledge. Each of those entries opens by naming the part that will eventually own it, so that the later author knows what to check rather than what to assume.

The register retains every unresolved entry, and the count printed by validate:atlases is the current measure. It stands at 141 of 143, and the two that remain are worth naming, because they are what the rule below looks like in practice rather than an accident of scheduling.

Both belong to Part XXVIII and both are unwritten by decision. That part searched the corpus for a mechanism for each and did not find one. For radiation fog the corpus carries the practical advice — not through airport scanners, hand luggage if it must be — and nothing on dose, mechanism, or the CT equipment now used for cabin baggage. For bronzing, every corpus hit for a metallic sheen turns out to be a cyanotype, a metal substrate or bronze powder paint rather than a fresh silver-gelatin print. Both pages teach the discrimination and say the mechanism is unestablished.

The last two rows closed on 8 September 2026. Relay leakage glow and uneven f-stop test-strip bands had been waiting on Parts XVI and XVII, which are written; both entries now carry the arithmetic those parts published, and in each case the arithmetic says the obvious suspect is not the cause — a switched-off solid-state relay delivers tens of milliwatts to a lamp that needs 150, and an f-stop rounding error is a fortieth of the smallest step a print can show.

An entry is published when its mechanism, its discriminating evidence and its corrective action are supported, not because an id exists in the plan. Nothing links to the four, because a link to an entry that will not be written is a promise the atlas cannot keep.

The defects

Alternative processes

• Albumen crazing and yellowingStage storage, handling, fixing, washingLikely causes Variations in humidity, producing differential dimensional change between the albumen layer and the paper; Flexing, rolling or flattening a dry print, which cracks a shrunken layer; Residual fixer or atmospheric sulfur converting albumen-bound silver to silver sulfideA fine network of cracks across the surface and a yellow cast in the whites - one is an identification characteristic of the process and the other is its commonest deterioration.
• Albumen layer dissolving during sensitisingStage coating, materials, handlingLikely causes A second albumen coating applied without hardening the first, so the second bath dissolved it; A hardening step that used alcohol too strong or too dilute to coagulate the layer evenly; A sheet too dry at sensitisation, so it did not take up the silver solution properlyA coating that came off the sheet in the silver bath - albumen is water-soluble until something makes it insoluble, and on a double-coated paper that something is a separate step.
• Blotchy and streaked hand coatingStage coating, materialsLikely causes Sensitiser that does not wet the paper, so it beads and sits in the pores; A gritty sensitiser, in which sparingly soluble crystals have come out of solution; Too little solution, or a coating stroke that ran dry before the sheet was coveredBrush marks, streaks, dry patches and small white spots in a hand-coated sheet - four different faults with four different origins, only one of which is technique.
• Blotchy kallitype developmentStage development, coating, handlingLikely causes A print laid into the developer unevenly, so different areas began developing at different moments; A developer below the temperature its formula was written for; Sensitiser unevenly absorbed, so the developer met different amounts of it in different placesA kallitype that developed in patches - a print-out image that is barely there, a developer that works warm, and an image that appears the instant the sheet touches the tray.
• Blue fog in cyanotype highlightsStage materials, coating, safelight, development, washingLikely causes A sensitiser that had already decomposed before it was coated; A hostile chemical in the paper reducing the sensitiser; Safelighting inadequate for the conditions of workingPrussian blue where there should be paper - and Ware's six-cause algorithm, which finds the culprit by asking at which stage the tone first appeared.
• Bronzing and reversal from cyanotype over-exposureStage exposure, washingLikely causes Exposure carried well past the point at which the shadows reach maximum density; A sensitiser variety that reverses strongly, used as though it did not; Judging exposure by the print-out image rather than by the finished printShadows that went pale instead of dark, and a bronze surface before the wash - one of those is solarisation and the other is what a correctly exposed cyanotype looks like.
• Cross-contamination between alternative processes sharing a benchStage coating, development, handling, materialsLikely causes A brush, rod, pipette or tray used for more than one process; Two sensitisers mixed, deliberately or by residue, whose ions are incompatible; The developer of one process used on the print of anotherBlue where there should be brown, white spots where there should be tone, and a developer that bleaches the wrong image - the faults of running several iron processes in one room.
• Cyanotype bleached by alkaline wash water or buffered paperStage washing, materials, storageLikely causes Paper or board carrying an alkaline buffer such as calcium carbonate; Alkaline wash water, or a wash that raised the pH; An alkaline mount, mat or storage enclosure in contact with the printA blue image that faded to nothing and left a yellow-brown stain behind - alkali hydrolyses Prussian blue irreversibly, and a pH of 9.4 is enough.
• Edge fading from mount and adhesiveStage storage, handlingLikely causes A mounting board with a lignin-rich core, whose decomposition products migrate through the top layer; A mounting adhesive that has decomposed, such as a putrefied starch or gelatin paste; A mat, window or frame backing in contact with the print, releasing oxidising or acidic productsA print that faded in a band around its edges, or under a mat, while the covered oval stayed clean - the mount is part of the chemistry, and lignin is the usual culprit.
• Iron-silver highlights that will not clearStage washing, materials, coatingLikely causes Unreduced silver left in the highlights that the wash alone will not remove; Iron(III) bound to the cellulose, which needs a chelating bath rather than water; A wash too short, too cold, or in water too hardA Van Dyke or kallitype whose whites stay yellow-brown however long they are washed - unreduced silver and bound iron, and two different residues that need two different baths.
• Mottled coating from uncontrolled humidityStage coating, materials, storageLikely causes Paper coated or printed before it had equilibrated with the room's humidity; A deliquescent sensitiser taking up water in a humid room and staying tacky; Very dry conditions, which change the image colour and the amount of print-outA hand-coated sheet whose tone and evenness change with the weather - humidity is a processing variable in the iron processes, and an uncontrolled one is an uncontrolled print.
• Negative poppingStage equipment, exposure, handlingLikely causes A glassless carrier at a high magnification, where the film is gripped at its edges and has nowhere to expand but out of the plane; A negative put in the carrier cold, focused at once, and exposed while it is still warming to the lamphouse's temperature; A tungsten head, whose filament emits far more infrared than visible light and sends almost all of it through the negativeA print whose fine detail is present but weak, veiled at hard edges and faintly doubled, in a band that lands somewhere different on every sheet - the negative moving in the heat of the beam part way through the exposure, and the one test that changes only its temperature.
• Newton's ringsStage equipment, exposure, handlingLikely causes A glass negative carrier whose plain glass comes within a wavelength of the smooth film base over part of the frame; A contact printing frame closed hard enough, or backed softly enough, that the base and the glass reach near-perfect contact across a wide area; Anti-Newton glass fitted with its textured face away from the film, so the texture prints and the fringes form anywayClosed, irregular grey loops on the print, like contour lines, that were never on the negative - the fault that forms where contact between film and glass is almost perfect, and the one test that separates it from a stain.
• Platinum print stain from incomplete clearingStage washing, materialsLikely causes Iron(III) chemisorbed onto the cellulose and not removed before the print dried; A clearing bath at the wrong pH for the iron it is meant to chelate; Hard water or a chalk-buffered paper, precipitating calcium oxalate and promoting hydrolysisYellow that appears in the highlights weeks after the print was finished - iron bound to the cellulose, and a three-bath sequence whose order is chemistry rather than convention.
• Prussian blue bleeding into the highlights by peptisationStage washing, coating, exposureLikely causes Excess ferrous iron produced in heavily exposed areas diffusing into adjacent highlights; Peptisation of Prussian blue by ions of high ionic strength, carrying pigment out of the paper; Redundant non-image pigment released into the wash and re-depositing on the picture areaBlue that spread out of the shadows into the whites - and two mechanisms that Ware keeps apart, only one of which is peptisation.
• Silver mirroring and sulfiding in an untoned printed-out printStage storage, washing, fixingLikely causes An untoned image of colloidal silver, unprotected by conversion to a more stable compound; Residual thiosulfate and silver-thiosulfate complexes from inadequate fixing and washing; Oxidising gases in the atmosphere, or in the framing and mounting materialsA metallic sheen by reflected light and a general loss of image by transmitted light - two different attacks on the same very finely divided silver, and toning is the answer to both.
• The gold toner that did nothing because the first wash was omittedStage washing, handlingLikely causes The pre-toning rinse omitted, so excess silver went into the toning bath with the print; A gold bath already spent, because each print consumes gold from it; A dry print put into the toner without soaking, so the toner never reached the imageA print that sat in an expensive bath and came out the colour it went in - the two-minute rinse before the toner is not a formality.
• The iron-silver print that faded within weeksStage washing, storage, materialsLikely causes Residual iron left in the image, which is deposited as insoluble ferric hydroxide and causes fading; Residual thiosulfate and silver-thiosulfate complexes from an inadequate fixing and washing; An untoned colloidal silver image, unprotected by a binder, on plain paperA Van Dyke or kallitype that lost its shadows in a month - residual iron catalysing the destruction of the image it helped to make.
• The printed-out image that bleached away in the fixerStage fixingLikely causes A fixing bath too strong, too long, or of the wrong kind for an unprotected silver image; Toning after fixing rather than before it, so the image met the hypo unprotected; Under-exposure, on a process that must be over-printed to survive processingA rich purple print that went pale and thin in the hypo - the fixer dissolving the image as well as the unexposed salt, and the two ways of stopping it.
• Uneven contact print from pressure, glass or source geometryStage equipment, exposure, handlingLikely causes Non-uniform pressure in the frame, so the gap between the two emulsions is not zero everywhere; Curl, grit, a bowed back or foam that has taken a set, holding the sandwich open in one region; Glass too thin to resist bowing, not flat, or carrying an anti-Newton texture that printsA proof sheet with dark corners, a regular stripe, or soft patches in an otherwise sharp frame - three unrelated faults sharing one complaint, separated by taking the negative out and printing the light on its own.
• Weak cyanotype maximum densityStage coating, washing, exposure, materialsLikely causes Image substance peptised and washed out during wet processing; Sensitiser poorly absorbed, so the pigment formed in the pores rather than in the fibres; A formulation too dilute in ferricyanide to reach a pictorial maximum densityA blue that will not go deep - image substance washing out of the paper, a sensitiser too dilute in ferricyanide, or an exposure scale that ran out three stops in.
• Yellow iron stain in cyanotype highlightsStage washing, coating, materialsLikely causes A wash too short, too cold or in too little water to remove the unexposed sensitiser; Hydrolysis of iron(III) to an insoluble yellow hydrated oxide in a wash that is not acidic enough; Sensitiser that sat on the surface rather than in the fibres, and then bound to themA yellow rather than blue tone in the whites - residual iron salts that the wash did not remove, which is a clearing fault and not a fogging one.
• Yellow-brown highlight stain from residual silverStage fixing, washing, storageLikely causes Silver bound to the binder in non-image areas, which fixing does not remove; Residual fixer decomposing and supplying sulfur to that bound silver; Atmospheric sulfur compounds reaching the print in storageWhites that went yellow while the image stayed put - silver bound so tightly to the binder that hypo cannot reach it, and a stain that no known treatment removes.

Emulsions and coatings

• Age fogStage materials, storageLikely causes Time, which lets grains acquire developable centres without any exposure; Storage above the maker's recommended temperature, which accelerates it; High humidity in storageA raised floor on a film that was never exposed to anything — grains that became developable with time rather than with light, and the reason the first symptom is muddy shadows rather than a thin negative.
• Base fogStage materials, storage, safelight, developmentLikely causes The material itself, from age, heat or over-ripening; A safelight, a light-tight box or a handling routine that is not light-tight; A developer that has gone over the alkali ladder or is contaminatedDensity where nothing was exposed, present on a control sheet that never went in the camera - the zero against which every other fault on a sheet is read.
• Black spotsStage materials, coatingLikely causes Pepper, a coarse grain reduced to metallic silver without any exposure to light; Undissolved halide that developed out as a black slug; Rust or another metallic contaminant in contact with the silver solutionFine black dots through the image and through the unexposed areas too, sometimes invisible to the naked eye - pepper and slugs, which look alike and are not the same fault.
• BlistersStage stop, fixingLikely causes Carbon dioxide evolved when a carbonate-bearing developer meets an acid bath; A fixing bath carrying an excess of acid, together with insufficient rinsing before it; A strongly acid rinse bath used between developer and fixerGas evolved inside a soft gelatin layer, lifting it — a mechanism Kodak stated in 1928 and confirmed in 1944 by selling an alkali that avoids it, and which on dry film looks like a field of tiny craters in reflected light.
• Bubbles and pinholes in a coatingStage coatingLikely causes Air whipped into the melt by stirring too vigorously or by shaking the bottle; Emulsion poured from a height rather than down the vessel wall; Air trapped under the layer as it was laid and never chased outClean round holes with no rim, made by air whipped into the melt or trapped under the layer as it was laid.
• Chemical fogStage developmentLikely causes Too much alkali, or a stronger alkali substituted for the one the formula names; Development carried far past the point where fog rises faster than image; A developer contaminated with something that raises its energyDensity on a patch that saw no light at all, produced by the developer rather than by the exposure - and which points up the alkali ladder rather than down it.
• Coating mottle and drying marksStage coating, dryingLikely causes A draught blowing directly on a drying sheet; A warm spot, or contact with the drying rack, drying part of the sheet faster than the rest; A change in the support the coater did not make, such as a paper whose sizing recipe was altered by its makerA soft irregular texture like a watermark, absent when the sheet was wet and present when it was dry, which is the whole of the diagnosis.
• CometsStage coating, materialsLikely causes Undissolved halide caught under the coating rod; A fragment of undissolved gelatin in the melt; A fibre or other solid picked up from the room or the vesselA dark or light head with a tail trailing behind it in the direction of the coating stroke, made by one solid particle caught under the rod.
• FrillingStage development, fixing, washing, coatingLikely causes Adhesion failure at the emulsion-support interface, worst at a free edge; Baths differing in temperature, or a bath run warm; A support that was contaminated, unsubbed or inadequately cleanedThe layer lifting, rolling back or detaching at the edges during processing, and the sourced remedy that is a hardening fixer rather than a hardener in the emulsion.
• Heat fogStage materials, storageLikely causes Storage above the maker's stated temperature, briefly or for a season; A film left in a hot vehicle, a loft, a conservatory or beside a radiator; High humidity together with heat, which the makers name as a pairThe same fault as age fog, arriving in an afternoon instead of a decade — and the reason a glovebox in summer is worse for a film than a year in a cupboard.
• PinholesStage coating, exposure, stop, fixingLikely causes Gas evolved inside a soft layer where a carbonate developer met an acid bath; A bubble or a dust particle trapped in a hand-coated emulsion before it set; A dust particle lying on the plate at the moment of exposure, masking the lightOne name for three unrelated faults — a gas crater, a bubble in a hand-coated layer, and the shadow of a dust particle — told apart by their edges and by the company they keep.
• Repellency spotsStage coating, handlingLikely causes Grease from a bare finger on the support before coating; Silicone, aerosol overspray or hand cream on the support or in the air; A support cleaned with detergent that left a residueRound bare patches with a raised rim where the wet layer retreated from a low-energy contaminant, and the one observation that separates them from air bells.
• ReticulationStage development, stop, fixing, washingLikely causes Solutions differing sharply in temperature, so the gelatin expands or contracts suddenly; A bath run at an extreme temperature; An unhardened or lightly hardened layer taken through a large temperature stepA coarse wrinkling all over the film from sudden swelling or contraction of the gelatin - a certain mechanism and a genuinely disputed reachability on modern materials.
• Safelight fogStage safelight, handlingLikely causes A safelight filter of the wrong class for the material being handled; Too long under the safelight, or too close to it; A material whose sensitivity extends into the colours the filter transmitsA uniform veil right to the cut edge of the sheet, present on the control that never went in the camera - and which often shows first as a loss of contrast rather than as visible fog.
• Thin coatStage coating, materialsLikely causes Too little emulsion laid down per unit area; A melt too dilute in gelatin to hold its thickness, often after noodle washing; A coating rod set closer to the sheet than the intended coating weight requiresA weak, low-contrast print that reads as a poor maximum black and is a coating fault - the trap that sends a coater back to change an emulsion that was never wrong.
• Under-fixingStage fixingLikely causes Fixing time shorter than twice the clearing time; A bath near exhaustion, so that silver leaves the grain as the sparingly soluble first complex; A thick or unevenly coated layer the fixer could not penetrateMilkiness or opalescence in the clear areas, which is the definition of the endpoint fixing did not reach - rescuable today, and invisible in its mild form until the third year.
• Uneven coating thicknessStage coatingLikely causes A bed that is not level, so the wet layer flows before it sets; Emulsion coated too warm, so it stays fluid long enough to flow; Too little gelatin for the volume, so the layer will not hold its thicknessA gradient with no edge to it - a heavier bottom, a heavier corner or a wedge - read for free in the fixing tray, because a plate clears last where it is thickest.

Instruments

• Balance drifting, or reading below its minimum weighable massStage equipment, materialsLikely causes A draught, an unlevel surface, or a leaning elbow on the bench; Static on a light powder; A quantity too small for the balance's resolution and repeatabilityA reading that creeps, or a weighing whose uncertainty is a fifth of the quantity - and the reason the course quotes no minimum weighable mass at all.
• Control chart: contaminationStage development, handlingLikely causes Fixer or stop bath carried into the developer on hands, tongs or a shared vessel; Mixing equipment that was not thoroughly cleaned between solutions; Dry chemical made airborne during mixing and settling into an adjacent solutionA chart that moves in a way none of the other signatures explains - and an entry that states, rather than fills, the gap where a measured figure ought to be.
• Control chart: developer exhaustionStage development, storageLikely causes Bromide and other by-products accumulating in a reused bath and restraining development; Aerial oxidation of a stock in a part-filled bottle, consuming the developing agents; A reuse compensation that is too small for the subjects actually being processedA chart that falls - a trend rather than an outlier - and the two different exhaustions, bromide accumulation and aerial oxidation, that the fog row tells apart.
• Control chart: temperature errorStage developmentLikely causes A developer mixed or tempered at the wrong temperature; A tank cooling towards room temperature during development; A thermometer read once at the start, or read at the wrong place in the bathA single point off aim, contrast first and furthest - the signature a bath two degrees warm leaves on a process control chart, and how it separates from the faults it resembles.
• Densitometer: ambient leakStage equipmentLikely causes Room light entering past the shroud or its seal; Open or lifted box seams around the sample stage; A sample larger than the shroud, holding the seal openReadings that change when the desk lamp is switched on - room light finding its way inside the shroud, which is a different fault from stray light and has a different cure.
• Densitometer: drifting zeroStage equipmentLikely causes Amplifier output offset moving with temperature, which matters most at the dense end; Lamp or detector still warming up, so the air reading has not settled; A dark reading taken once at switch-on instead of with every measurementAn instrument whose readings creep through a session - the scale shifted without being bent, and the amplifier offset that moves with room temperature is the usual reason.
• Densitometer: high-density compressionStage equipmentLikely causes Light from the instrument's own lamp reaching the detector without passing through the sample; An unblackened or unbaffled interior, an open box seam, or a reflective arm underside; An aperture plate too thick or too wide for the sample, spreading the acceptance coneA scale that is faithful for two decades and then bends over - the signature of stray light, which adds a fixed quantity to every reading and caps the instrument at the negative logarithm of its own floor.
• Densitometer: scale errorStage equipmentLikely causes A reference density that is not what it was assumed to be; A gain or a full-scale value misread, so every reading is scaled by a constant; A wedge whose nominal increment is not its actual incrementEvery density low by about the same fraction - a calibration fault rather than a range fault, and one that black paint will not fix.
• Lamp glowing faintly between exposures, from a switching device that leaksStage exposure, safelight, equipmentLikely causes A solid-state switched output passing its rated off-state current through the lamp; A faulty switching device passing far more than its rated off-state current; A load that is not a tungsten filament responding to a few milliampsAn enlarger lamp that never goes fully dark between exposures, from a switched output that leaks when it is commanded off - what it can and cannot do to paper, and why the test is a sheet of paper rather than a meter.
• pH meter reading a constant valueStage equipmentLikely causes The bulb is not fully immersed, or the protective cap is still on; A loose or damp connector giving a dead, stable, plausible mid-scale reading; A cracked bulb short-circuiting the two half-cells through the crackOne number in the buffer, in the tap water and in the stop bath - the checks that separate an electrode out of the liquid from an electrode that is dead.
• Session exposure driftStage exposure, development, equipmentLikely causes A light source still warming, whose output falls as its junction or filament temperature rises; Supply variation, or a lamp fed from a circuit doing other work; A print developer exhausting on the work it has donePrints that get darker or lighter through an evening at the same nominal exposure - a lamp warming, a supply sagging, or a developer working itself out, and one test that tells the three apart.
• Uneven density across a stripStage equipment, development, exposureLikely causes A non-uniform exposing field in the sensitometer, so the strip was never evenly lit; Poor contact between the wedge and the film, so light spread under the steps; Uneven development - insufficient agitation, a crowded tank, or a strip lying against a wallA control strip whose steps are not the same density across their width - a fault that lives in the instrument, the wedge or the agitation rather than in the film, and which corrupts every curve read from it.

Negatives

• Age fogStage materials, storageLikely causes Time, which lets grains acquire developable centres without any exposure; Storage above the maker's recommended temperature, which accelerates it; High humidity in storageA raised floor on a film that was never exposed to anything — grains that became developable with time rather than with light, and the reason the first symptom is muddy shadows rather than a thin negative.
• Air bellsStage developmentLikely causes Air entrained when the developer was poured in, lodging against the emulsion; The tank not tapped on the bench after filling and at each agitation; A pour too slow or too turbulent, or a tank filled too farSmall, round, perfectly clear spots where a bubble sat against the emulsion and no developer reached it — and the one physical action both major manufacturers put in their published procedure to prevent them.
• Base fogStage materials, storage, safelight, developmentLikely causes The material itself, from age, heat or over-ripening; A safelight, a light-tight box or a handling routine that is not light-tight; A developer that has gone over the alkali ladder or is contaminatedDensity where nothing was exposed, present on a control sheet that never went in the camera - the zero against which every other fault on a sheet is read.
• Base-side scratchesStage handling, equipment, exposureLikely causes Grit in the cassette's felt light trap, drawn along the base at every wind; The camera's pressure plate or film path, worn or contaminated; Dirt in the camera, which a laboratory diagnoses and hands back to the customerA groove in clear plastic that has removed no silver at all — so it reads dark on a light box, prints white, and can often be made to vanish by filling it with something of the same refractive index.
• Bellows factor omittedStage exposure, equipmentLikely causes A frame added or removed to reframe, changing the focal distance and therefore the f-number; An exposure computed for one configuration and given in another; A configuration recorded in the log after the exposure rather than before itA thin negative because the frames were stacked to reframe and the exposure was not recomputed - the pinhole's version of the bellows factor, arriving as a changed f-number.
• BlistersStage stop, fixingLikely causes Carbon dioxide evolved when a carbonate-bearing developer meets an acid bath; A fixing bath carrying an excess of acid, together with insufficient rinsing before it; A strongly acid rinse bath used between developer and fixerGas evolved inside a soft gelatin layer, lifting it — a mechanism Kodak stated in 1928 and confirmed in 1944 by selling an alkali that avoids it, and which on dry film looks like a field of tiny craters in reflected light.
• Blocked highlightsStage exposure, developmentLikely causes Exposure that carried the brightest part of the subject past the top of the material's usable range; Development carried far enough to push the highlights onto the shoulder; A subject whose range exceeds what the material can hold, so no single exposure will fit itAn area that was bright in the subject and is now so dense that no detail can be seen in it - not recoverable, because the material stopped responding before the exposure ended.
• Blocked shoulderStage exposure, developmentLikely causes Over-exposure, which slides the whole subject up the exposure axis onto the shoulder; Over-development, which raises the upper scale until it reaches the coating's ceiling sooner; A subject whose luminance range is longer than the film's straight line at that developmentA curve that flattens early at the top - highlights running into one another on the negative because the exposure landed where the slope had already fallen away.
• Bromide dragStage developmentLikely causes Reduced or absent agitation, letting spent developer sink from the dense areas; Long, dilute, nearly unagitated development, where the effect is the intended mechanism arriving as a fault; A tank or tray left standing between agitation cycles for too longStreaks running downward from the dense parts of a negative, made by spent developer that is denser than the bulk and sinks, retarding development in whatever it flows over.
• Buckled-sheet softnessStage equipment, exposure, handlingLikely causes Insufficient pressure on the sheet in the back, so it bows towards the hole; Resin-coated paper from a freshly opened packet, which curls more than paper that has settled; A pressure plate with foam that has compressed with ageA denser centre, subtly bowed straight lines and a middle that is very slightly sharper - a density fault masquerading as a sharpness fault.
• Burr smearStage equipment, exposureLikely causes A lip of material pushed up on the far side when the plate was pierced; A hole finished from one side only, so the burr was never abraded off; A plate reworked after measurement, leaving a ragged flap in the light pathSoftness with a preferred direction that is the same at every point in the frame, from a lopsided aperture - and the one comparison that tells it from movement.
• Calcium scumStage washing, dryingLikely causes A hard water supply, whose dissolved calcium and magnesium are left behind as the last water evaporates; A final rinse made with tap water in a hard-water district; Too much wetting agent, which adds its own dissolved solid to what is left behindA whitish film left on a dried negative or print by hard water, and the two manufacturer answers that have not changed in eighty years — distilled water for the final rinse, and less wetting agent rather than more.
• Chemical fogStage developmentLikely causes Too much alkali, or a stronger alkali substituted for the one the formula names; Development carried far past the point where fog rises faster than image; A developer contaminated with something that raises its energyDensity on a patch that saw no light at all, produced by the developer rather than by the exposure - and which points up the alkali ladder rather than down it.
• Cinch and pressure marksStage handling, exposure, equipmentLikely causes Pulling a loose film tight by turning the cassette spool; Forcing a film onto a spiral reel, or bending it while loading in the dark; Excessive tension in transport, in a camera or in a processorSharp crescents of extra density, made by force on the film before it was ever developed — a plus-density fault that is not a scratch, does not feel like one, and points at the loading rather than the tank.
• Control chart: contaminationStage development, handlingLikely causes Fixer or stop bath carried into the developer on hands, tongs or a shared vessel; Mixing equipment that was not thoroughly cleaned between solutions; Dry chemical made airborne during mixing and settling into an adjacent solutionA chart that moves in a way none of the other signatures explains - and an entry that states, rather than fills, the gap where a measured figure ought to be.
• Control chart: developer exhaustionStage development, storageLikely causes Bromide and other by-products accumulating in a reused bath and restraining development; Aerial oxidation of a stock in a part-filled bottle, consuming the developing agents; A reuse compensation that is too small for the subjects actually being processedA chart that falls - a trend rather than an outlier - and the two different exhaustions, bromide accumulation and aerial oxidation, that the fog row tells apart.
• Control chart: temperature errorStage developmentLikely causes A developer mixed or tempered at the wrong temperature; A tank cooling towards room temperature during development; A thermometer read once at the start, or read at the wrong place in the bathA single point off aim, contrast first and furthest - the signature a bath two degrees warm leaves on a process control chart, and how it separates from the faults it resembles.
• Cut-off toeStage exposure, materialsLikely causes Under-exposure, which places the subject's shadows below the threshold exposure; A speed rating higher than the film delivers in this developer; An exposing instrument or wedge whose lowest steps deliver less than they claimA curve that starts abruptly instead of easing up from the floor - shadow detail that was never recorded, because the exposure fell below the film's threshold.
• Dense negativeStage exposure, development, materialsLikely causes Overexposure, which raises the shadows as well as everything else; Over-development, from time, temperature, concentration or agitation; Fog on top of an otherwise correct negative, which raises the floor rather than the pictureEverything dark, including the shadows — and the one reading that says whether the camera gave too much light or the tank gave too much development.
• Dense negative from double correctionStage exposureLikely causes A published correction applied to a time that had already been corrected; Two people, or two passes, each correcting the same metered time; A corrected time written into the metered-time field of the logA dense negative with blocked highlights produced by applying a published reciprocity correction twice - the error that hides best, because every individual step was done correctly.
• Developer contaminated by fixer or stopStage development, materialsLikely causes A graduate, funnel, stirrer or thermometer used for two baths without washing; Tongs moved between trays, or a hand that had been in the fixer; A bottle refilled from the wrong jug, or an unlabelled vesselTwo contaminations that arrive by the same route and behave nothing alike — a trace of thiosulfate, which the makers say to discard the bath over, and a splash of acid, which merely makes it slow.
• Developer stainStage development, stop, handlingLikely causes Developer left on the material at a transfer, drying in air before it reached the stop bath; A sheet or a film only partly covered by the solution; Developer on a hand, a tong or a bench, transferred to dry paperA brown mark where developer was left on the material and oxidised in air — an edge, a drip, a fingerprint or a whole sheet — and the two observations that separate it from the stain a staining developer leaves on purpose.
• Dichroic fogStage development, fixingLikely causes Developer carried into the fixing bath without a rinse or a stop bath; An old, exhausted fixer already carrying an excess of dissolved silver; A silver-halide solvent in the developer meeting carried-over reducing agent inside the gelatinA veil that is greenish by reflected light and reddish-pink by transmitted light - finely divided metallic silver, which prolonged immersion in hypo does not mend.
• Diffraction glow from an undersized hole on paperStage equipment, exposureLikely causes A hole smaller than the optimum for the focal distance in use; A hole reduced below its band by abrading a burr off it; A plate chosen for a long focal distance and used at a short oneA soft glow spilling across every edge rather than a plain blur, because the hole is smaller than the optimum and the blur figure now has a bright core with far-reaching tails.
• Dilution ratio misread as a fractionStage materialsLikely causes A colon notation read as a ratio to the finished volume rather than to the water; A sheet writing 1+10 transcribed as 1 to 10 and then made up to ten parts; A formula copied from a secondary source that changed the notationA working solution about ten per cent out because a colon was read as a ratio to the total rather than as parts of stock to parts of water.
• Double image from a reflective plateStage equipment, exposureLikely causes A pinhole plate blackened on the outside face only; A bare metal plate used as made, with no blackening at all; A plate whose blackening has been abraded off the inside face by handlingA faint, broad, displaced ghost of the frame's own bright areas, thrown back by the unblackened inside face of the pinhole plate - described from the geometry, because the course has not photographed one.
• Drying marksStage dryingLikely causes No wetting agent in the final rinse, so the film dries as drops rather than as a sheet; A wetting agent wrongly diluted — too little or too much; Hard water, which leaves more dissolved solid behindNot dirt on the gelatin but a change in it, left where the last of the water evaporated and everything dissolved in it stayed behind — with five causes, five published corrective actions, and an honest limit on what can be undone.
• Edge leakStage equipment, exposure, handlingLikely causes Light entering at a body seam or corner and spreading inside the camera; The mouth of the dark-slide slot admitting light around the slide; A joint that runs the length of an edge and was never light-trappedA broad soft band along one edge of the sheet, densest at the edge and fading inwards, which continues under the strips the paper stops covered.
• Elevated fog on a curveStage materials, storage, safelight, developmentLikely causes Film that has aged, been stored warm, or been near a radiation source; A developer pushed too far, too warm, or short of its restrainer; A light leak or an unsafe safelight adding a uniform small exposureA curve whose whole floor has lifted - D-min above aim, highlights compressed, and the four sources of unwanted density that a control strip can tell apart.
• Empty shadowsStage exposure, developmentLikely causes Underexposure, so the darkest parts of the subject never made a developable centre; A reciprocity correction omitted or taken from the wrong material; A subject whose range exceeds what the material can holdAn area that was dark in the subject and is now indistinguishable from clear film base, with nothing in it - the unrecoverable failure at the other end of the scale.
• Emulsion-side scratchesStage development, washing, drying, handlingLikely causes A squeegee or chamois with grit caught in it; Contact with a rough surface while the emulsion was swollen and soft; Dirt or chemical build-up on rollers, racks or squeegees in a processorA groove cut into the layer that carries the picture, so silver has actually been removed — which is why it prints black, why no fluid will hide it, and why it convicts the wet side of the process.
• Excessive contrastStage development, exposure, materialsLikely causes Development carried too far, by time, temperature, concentration or agitation; A subject whose own luminance range was longer than the process could hold, which is not a fault; Underexposure with normal development, which raises apparent contrast by putting the shadows on the toeShadows correct, highlights impenetrable, and no grade of paper that holds both — the signature of development carried too far, and of the two impostors that look exactly like it.
• Exhausted developerStage development, materialsLikely causes More film or paper put through the bath than its published capacity allows; No time compensation applied as the running total rose; A working solution reused past the point where its by-products restrain itA thin, flat strip with a fog floor lower than the control's - the one discriminator that separates a bath that has done too much work from a bath that has merely oxidised.
• Exhausted fixerStage fixingLikely causes More material put through the bath than its published capacity allows; No clearing-time test on a schedule, so the bath was judged by appearance; Developer carried in without a rinse or a stop bath, spending the acid and the sulfite reserveA bath whose clearing time has doubled, whose curve is flat for two thirds of its life, and which fails by leaving something invisible behind rather than by refusing to work.
• Fingerprints on paperStage handling, development, fixingLikely causes A hand that had been in the fixer touching unexposed or undeveloped paper; A hand that had been in the developer touching dry paper; Handling wet prints by the surface rather than by the edgeA print of the ridges of a finger, made of chemistry rather than grease — white if the hand had been in the fixer, dark if it had been in the developer, and permanent either way.
• Fixer contaminated by developerStage fixing, stopLikely causes No stop bath and no rinse between developer and fixer; A water rinse used too many times without being changed; Prints, which carry far more developer than film doesThe one contamination that happens on every film you process — the question is only how much — and the three separate faults that carried-over alkaline developer produces in an acid bath.
• Flare veilStage equipment, exposureLikely causes A shiny or light-coloured camera interior returning light that missed the film; An unblackened pinhole plate reflecting light back onto the sheet; A bright source just outside the frame, striking the interior walls at a shallow angleCorrect overall density with flat grey shadows and clean highlights, from light that came through the hole and bounced off the interior - and which stops dead at the paper stops.
• Flat negativeStage development, exposureLikely causes Under-development, which lowers contrast and density together; Non-image light lifting the shadows, from flare, a leak, a safelight or fog; A subject with less range in it than the reading assumedFewer separable steps between the first density and the maximum, which usually travels with thinness and together with it is the signature of under-development.
• Frame-to-frame density variationStage exposure, equipmentLikely causes Metering that responded to a different part of each scene; A shutter whose error varies with the speed selected, or which sticks intermittently; An aperture mechanism that does not close consistentlyOne roll, one bath, one time — and frames that do not match each other. Everything the whole film shared is thereby eliminated, which is what makes this fault unusually easy to place.
• FrillingStage development, fixing, washing, coatingLikely causes Adhesion failure at the emulsion-support interface, worst at a free edge; Baths differing in temperature, or a bath run warm; A support that was contaminated, unsubbed or inadequately cleanedThe layer lifting, rolling back or detaching at the edges during processing, and the sourced remedy that is a hardening fixer rather than a hardener in the emulsion.
• Geometric softness from an oversized holeStage equipment, exposureLikely causes A hole larger than the optimum for the focal distance in use; A plate chosen for a short focal distance and used at a long one; A hole enlarged by piercing further than intended and never re-measuredPlain, even, flat-topped blur across the whole frame, the same in every direction, because the hole is larger than the optimum for the focal distance it is being used at.
• Hardener sludgeStage fixingLikely causes Too little acid in the hardener, or the wrong strength of acid used in mixing; Developer carried over into the bath, neutralising the acid that was there; A bath exhausted, still carrying alum and sulphite but no acidA white gelatinous precipitate of aluminium sulphite in an alum fixing bath, or a white scum of it on the material — a fault of too little acid rather than too much, with three named causes and one published removal.
• Heat fogStage materials, storageLikely causes Storage above the maker's stated temperature, briefly or for a season; A film left in a hot vehicle, a loft, a conservatory or beside a radiator; High humidity together with heat, which the makers name as a pairThe same fault as age fog, arriving in an afternoon instead of a decade — and the reason a glovebox in summer is worse for a film than a year in a cupboard.
• Hot spotStage equipment, exposureLikely causes A bright, flat interior wall reflecting specularly rather than diffusely; A source just outside the frame striking that wall at a shallow angle; An interior finish that is matt to the eye and glossy at grazing incidenceA bright patch on the negative near one edge, roughly the shape of the interior wall it reflected from and always on the side away from the source - described here from the geometry, because the course has not photographed one.
• Hydrate substituted for an anhydrous salt at the same massStage materialsLikely causes The jar on the shelf is a different hydrate from the one the formula names; A pre-1950 formula whose unqualified names mean the crystallised forms; A formula that names a salt without stating its hydrate state at allA developer 2.7 times too alkaline, or a fixer well under strength, because water of crystallisation was weighed as though it were the salt.
• Hypo spots on unexposed paperStage handling, materialsLikely causes A splash of fixer reaching the paper box, the easel or the dry bench; A hand that had been in the fixer touching unexposed paper; Wet fingers or tongs handling paper on the dry sideWhite marks that no exposure can fill, because the silver halide under them was dissolved before the enlarger was ever switched on — a bench fault rather than a bath fault, and completely unrecoverable.
• Insufficient solution volumeStage development, fixingLikely causes A spiral tank filled below the top of the film; A dish with too shallow a layer for the size of print; A volume scaled down without scaling the capacity down with itA tank or a dish with too little in it, which produces three different faults at once — a tide line where the solution ended, unevenness where it was shallow, and a bath exhausted before its published capacity.
• Light-leak fogStage equipment, handling, storageLikely causes A leak in the camera body, the shutter or the dark slide; A film or paper box that is not light-tight; A loading routine carried out where light could reach the materialFog that came in through a hole rather than through the picture - identified by whether it crosses the parts of the sheet the picture could never reach.
• Low contrast indexStage development, materialsLikely causes Development too short, too cool, or too gently agitated for the film and developer; A developer that has lost activity - oxidised in a part-filled bottle, or restrained by accumulated bromide; A developer or dilution whose normal slope is lower than the one being aimed atA characteristic curve whose straight line is too shallow - a negative that measured flat rather than merely looked it, and the four causes a measurement can separate.
• Motion smearStage exposure, handlingLikely causes The camera moved, from wind on the tripod or a knock; The subject moved, which on an exposure of minutes is normal for leaves, water, cloud and people; The shutter jarred the camera at one end of the exposureThe one kind of unsharpness that cares which way an edge runs - and the single loupe comparison that separates every movement fault from every optical one.
• Mottled developmentStage developmentLikely causes Inadequate agitation, so that depletion patterns survive across the frame; A semi-stand or reduced-agitation regime taken further than the material tolerates; Solution volume too small for the surface being developedAreas of non-uniform density with no direction to them, which manufacturers put squarely against inadequate agitation - the opposite end of the same lever from surge marks.
• Near-limit softnessStage exposureLikely causes The nearest subject sitting closer than the configuration's near limit; A near limit never computed for the focal distance in use; A still life or portrait framed at a distance chosen for composition aloneOne object soft with everything behind it as sharp as the camera ever gets, because the blur circle grows as the subject comes closer and a pinhole has no focus to lose.
• Over-fixingStage fixingLikely causes Fixing paper for the film time, which is two to five times too long; Leaving prints in the fixer while other work is finished; A rapid fixer at a film dilution used on paperThe fixer dissolving the picture as well as the halide — highlights first, because the deposits there are smallest, and paper first, because its published time is a fraction of film's.
• Oxidation stainStage development, stop, fixingLikely causes Material moved from developer to fixer with little or no rinsing; A fixer whose sulfite has been used up and whose acid has been neutralised; Developer allowed to oxidise on the surface of the material before it reached the next bathA brown or yellow-brown general stain present from the first day, from developer carried into a fixer with too little sulfite and acid left to deal with it.
• Oxidised developerStage storage, materials, developmentLikely causes A bottle stored with a large headspace, so that every opening presented a fresh air interface; A stock kept beyond its published storage life; A tray or open tank left standingAn amber or brown solution that gives a thin, flat negative with a normal fog floor - and the asymmetry that matters, which is that colour convicts and clear does not acquit.
• PinholesStage coating, exposure, stop, fixingLikely causes Gas evolved inside a soft layer where a carbonate developer met an acid bath; A bubble or a dust particle trapped in a hand-coated emulsion before it set; A dust particle lying on the plate at the moment of exposure, masking the lightOne name for three unrelated faults — a gas crater, a bubble in a hand-coated layer, and the shadow of a dust particle — told apart by their edges and by the company they keep.
• Reel and contact marksStage development, handlingLikely causes Film touching itself where a spiral was loaded badly or the reel was damp; Two turns of film pressed together on an over-filled reel; Sheets shuffled in a tray, pressed face to back so that solution is squeezed outBroad, soft, pale patches where two surfaces touched and no solution could get in — the fault of a badly loaded spiral or a shuffled stack, and how it differs from the crescent that force leaves behind.
• Residual silver and yellow stainingStage fixing, washing, storageLikely causes An exhausted fixer leaving the sparingly soluble first silver-thiosulfate complex in the paper; Fixing time too short for the material and the bath; A single fixing bath used where two were neededA yellowing that was not there when the print dried, strongest in the borders and highlights - the retained complex sulfiding, and the geography of the stain is a map of where the halide was.
• Residual thiosulfateStage washing, fixingLikely causes A wash too short, or one in which the water was not actually changing; A fibre-base paper washed as though it were resin-coated; Fixing carried far past the point needed, driving solution into the paper baseThiosulfate left in the layer after washing, invisible at the time, which supplies the sulfur that turns image silver into silver sulfide - and the silver nitrate test that finds it.
• ReticulationStage development, stop, fixing, washingLikely causes Solutions differing sharply in temperature, so the gelatin expands or contracts suddenly; A bath run at an extreme temperature; An unhardened or lightly hardened layer taken through a large temperature stepA coarse wrinkling all over the film from sudden swelling or contraction of the gelatin - a certain mechanism and a genuinely disputed reachability on modern materials.
• Room light leak, with a directionStage safelight, handling, storageLikely causes A gap around a door, a window, or a ventilator; A seam in the construction that is not opaque to visible light or to infrared; Light entering with a person, or from a device inside the roomFog that is heavier on one edge of the paper than the other - a leak has a direction, and the direction is what finds it.
• Safelight fogStage safelight, handlingLikely causes A safelight filter of the wrong class for the material being handled; Too long under the safelight, or too close to it; A material whose sensitivity extends into the colours the filter transmitsA uniform veil right to the cut edge of the sheet, present on the control that never went in the camera - and which often shows first as a loss of contrast rather than as visible fog.
• Safelight-fogged control stripStage safelight, handlingLikely causes A safelight filter that is wrong, faded or cracked for the material in use; Too high a bulb wattage, too short a distance, or too many safelights; Handling time longer than the material's safe time under that illuminationA control strip whose D-min has risen and whose highlights have closed up, with speed and contrast almost untouched - the sensitometric signature of light that was supposed to be safe.
• Seam leakStage equipment, exposureLikely causes An unfilled screw hole giving a straight path from outside to the film; A crack or split in the body; A gap at a rebate where two panels meet without an overlapA sharp streak or wedge running in from a corner, which is a straight optical path - a screw hole, a crack or a gap at a rebate - rather than light spreading from an edge.
• Session exposure driftStage exposure, development, equipmentLikely causes A light source still warming, whose output falls as its junction or filament temperature rises; Supply variation, or a lamp fed from a circuit doing other work; A print developer exhausting on the work it has donePrints that get darker or lighter through an evening at the same nominal exposure - a lamp warming, a supply sagging, or a developer working itself out, and one test that tells the three apart.
• Shutter leakStage equipment, exposureLikely causes A sliding blade lying flat against the outside of the front panel rather than running in a rebated channel; A wedge-shaped gap at the blade edge that admits light at shallow angles; A shutter that was not fully closed between exposuresA band of raised density along the edge nearest the shutter, present on the capped-pinhole sheet and absent on the closed-shutter sheet, which is what identifies it and nothing else does.
• Silver mirroringStage storageLikely causes Oxidising gases from the atmosphere reaching the image silver; Poor-quality mount, mat or framing materials in contact with the print; Storage in an enclosure or climate that concentrates pollutants at the edgesA bluish metallic sheen starting at the edges and visible under reflected light, made by image silver that was oxidised, migrated to the surface and was reduced again there.
• Static discharge marksStage handling, exposure, equipmentLikely causes Rapid winding or rewinding of film in dry air, separating charge faster than it can leak away; Separating sheets or rolls quickly, especially interleaved sheet film; Low humidity in the space where film is handledBranch-like marks, spots with dark centres, or a row of dots — a photograph of an electrical spark, recorded by the film that made it, and told from a light leak by being sharp where a leak is graded.
• Surge marksStage developmentLikely causes Excessive or uneven agitation driving solution through the film perforations; A spiral tank inverted too vigorously or too often; Agitation applied in one direction only, so the flow pattern never changesA regular series of marks aligned with the sprocket holes of 35 mm film, from solution driven through the perforations by agitation - a mechanism the course states and a sourced identification it does not have.
• Thick-plate vignettingStage equipment, exposureLikely causes A pinhole plate thicker than about one fifth of the hole diameter; A hole drilled rather than pierced, leaving a parallel-sided bore; Steel shim used because it was what was in the drawerDark edges and corners with a comparatively hard boundary at a computable radius, because a hole in a thick plate is a short tunnel and beyond a certain angle no light passes at all.
• Thin negativeStage development, exposureLikely causes Under-development, from time, temperature, dilution or an exhausted bath; An oxidised or contaminated developer; Underexposure, which is a different fault with a similar appearance and is separated by one comparisonEvery step lighter than the control's, with the top steps never reaching a real black - and the single comparison that says whether it is the developer or the exposure.
• Thin negative from wrong reciprocity dataStage exposureLikely causes A reciprocity correction taken from a different manufacturer's sheet than the material in the camera; No correction applied at all to an exposure well beyond one second; A remembered exponent used in place of the published one for the material loadedA thin negative with empty shadows and a normal rebate, from a real correction correctly applied to the wrong material - and the log field that is the only thing that can find it.
• Timer display fogStage safelight, handlingLikely causes A timer, thermometer or exposure monitor with a lighted display facing the working surface; An indicator lamp on a power strip, a heater or a charger; A display bright enough at a wavelength the paper still responds toA faint patch of fog the shape of whatever was on the bench facing the paper - a lighted dial is a light source, and Kodak name it as one.
• Under-fixingStage fixingLikely causes Fixing time shorter than twice the clearing time; A bath near exhaustion, so that silver leaves the grain as the sparingly soluble first complex; A thick or unevenly coated layer the fixer could not penetrateMilkiness or opalescence in the clear areas, which is the definition of the endpoint fixing did not reach - rescuable today, and invisible in its mild form until the third year.
• Uneven density across a stripStage equipment, development, exposureLikely causes A non-uniform exposing field in the sensitometer, so the strip was never evenly lit; Poor contact between the wedge and the film, so light spread under the steps; Uneven development - insufficient agitation, a crowded tank, or a strip lying against a wallA control strip whose steps are not the same density across their width - a fault that lives in the instrument, the wedge or the agitation rather than in the film, and which corrupts every curve read from it.
• Water spotsStage washing, dryingLikely causes Drops of water splashed onto a film that was already drying; Drops running from clips, from a shelf above, or from a neighbouring film; A wetting agent wrongly diluted, so that the rinse breaks into drops rather than sheeting offDiscrete round or teardrop marks where single drops sat and dried, distinguished from the streaks of a drainage fault by their shape — and from dirt by whether they appear dark or light by transmitted light.

Plates

• Air bellsStage developmentLikely causes Air entrained when the developer was poured in, lodging against the emulsion; The tank not tapped on the bench after filling and at each agitation; A pour too slow or too turbulent, or a tank filled too farSmall, round, perfectly clear spots where a bubble sat against the emulsion and no developer reached it — and the one physical action both major manufacturers put in their published procedure to prevent them.
• Base fogStage materials, storage, safelight, developmentLikely causes The material itself, from age, heat or over-ripening; A safelight, a light-tight box or a handling routine that is not light-tight; A developer that has gone over the alkali ladder or is contaminatedDensity where nothing was exposed, present on a control sheet that never went in the camera - the zero against which every other fault on a sheet is read.
• Base-side scratchesStage handling, equipment, exposureLikely causes Grit in the cassette's felt light trap, drawn along the base at every wind; The camera's pressure plate or film path, worn or contaminated; Dirt in the camera, which a laboratory diagnoses and hands back to the customerA groove in clear plastic that has removed no silver at all — so it reads dark on a light box, prints white, and can often be made to vanish by filling it with something of the same refractive index.
• Black spotsStage materials, coatingLikely causes Pepper, a coarse grain reduced to metallic silver without any exposure to light; Undissolved halide that developed out as a black slug; Rust or another metallic contaminant in contact with the silver solutionFine black dots through the image and through the unexposed areas too, sometimes invisible to the naked eye - pepper and slugs, which look alike and are not the same fault.
• BlistersStage stop, fixingLikely causes Carbon dioxide evolved when a carbonate-bearing developer meets an acid bath; A fixing bath carrying an excess of acid, together with insufficient rinsing before it; A strongly acid rinse bath used between developer and fixerGas evolved inside a soft gelatin layer, lifting it — a mechanism Kodak stated in 1928 and confirmed in 1944 by selling an alkali that avoids it, and which on dry film looks like a field of tiny craters in reflected light.
• Bubbles and pinholes in a coatingStage coatingLikely causes Air whipped into the melt by stirring too vigorously or by shaking the bottle; Emulsion poured from a height rather than down the vessel wall; Air trapped under the layer as it was laid and never chased outClean round holes with no rim, made by air whipped into the melt or trapped under the layer as it was laid.
• Calcium scumStage washing, dryingLikely causes A hard water supply, whose dissolved calcium and magnesium are left behind as the last water evaporates; A final rinse made with tap water in a hard-water district; Too much wetting agent, which adds its own dissolved solid to what is left behindA whitish film left on a dried negative or print by hard water, and the two manufacturer answers that have not changed in eighty years — distilled water for the final rinse, and less wetting agent rather than more.
• Chemical fogStage developmentLikely causes Too much alkali, or a stronger alkali substituted for the one the formula names; Development carried far past the point where fog rises faster than image; A developer contaminated with something that raises its energyDensity on a patch that saw no light at all, produced by the developer rather than by the exposure - and which points up the alkali ladder rather than down it.
• Cinch and pressure marksStage handling, exposure, equipmentLikely causes Pulling a loose film tight by turning the cassette spool; Forcing a film onto a spiral reel, or bending it while loading in the dark; Excessive tension in transport, in a camera or in a processorSharp crescents of extra density, made by force on the film before it was ever developed — a plus-density fault that is not a scratch, does not feel like one, and points at the loading rather than the tank.
• Coating mottle and drying marksStage coating, dryingLikely causes A draught blowing directly on a drying sheet; A warm spot, or contact with the drying rack, drying part of the sheet faster than the rest; A change in the support the coater did not make, such as a paper whose sizing recipe was altered by its makerA soft irregular texture like a watermark, absent when the sheet was wet and present when it was dry, which is the whole of the diagnosis.
• CometsStage coating, materialsLikely causes Undissolved halide caught under the coating rod; A fragment of undissolved gelatin in the melt; A fibre or other solid picked up from the room or the vesselA dark or light head with a tail trailing behind it in the direction of the coating stroke, made by one solid particle caught under the rod.
• Developer stainStage development, stop, handlingLikely causes Developer left on the material at a transfer, drying in air before it reached the stop bath; A sheet or a film only partly covered by the solution; Developer on a hand, a tong or a bench, transferred to dry paperA brown mark where developer was left on the material and oxidised in air — an edge, a drip, a fingerprint or a whole sheet — and the two observations that separate it from the stain a staining developer leaves on purpose.
• Dichroic fogStage development, fixingLikely causes Developer carried into the fixing bath without a rinse or a stop bath; An old, exhausted fixer already carrying an excess of dissolved silver; A silver-halide solvent in the developer meeting carried-over reducing agent inside the gelatinA veil that is greenish by reflected light and reddish-pink by transmitted light - finely divided metallic silver, which prolonged immersion in hypo does not mend.
• Drying marksStage dryingLikely causes No wetting agent in the final rinse, so the film dries as drops rather than as a sheet; A wetting agent wrongly diluted — too little or too much; Hard water, which leaves more dissolved solid behindNot dirt on the gelatin but a change in it, left where the last of the water evaporated and everything dissolved in it stayed behind — with five causes, five published corrective actions, and an honest limit on what can be undone.
• Emulsion-side scratchesStage development, washing, drying, handlingLikely causes A squeegee or chamois with grit caught in it; Contact with a rough surface while the emulsion was swollen and soft; Dirt or chemical build-up on rollers, racks or squeegees in a processorA groove cut into the layer that carries the picture, so silver has actually been removed — which is why it prints black, why no fluid will hide it, and why it convicts the wet side of the process.
• FrillingStage development, fixing, washing, coatingLikely causes Adhesion failure at the emulsion-support interface, worst at a free edge; Baths differing in temperature, or a bath run warm; A support that was contaminated, unsubbed or inadequately cleanedThe layer lifting, rolling back or detaching at the edges during processing, and the sourced remedy that is a hardening fixer rather than a hardener in the emulsion.
• Hardener sludgeStage fixingLikely causes Too little acid in the hardener, or the wrong strength of acid used in mixing; Developer carried over into the bath, neutralising the acid that was there; A bath exhausted, still carrying alum and sulphite but no acidA white gelatinous precipitate of aluminium sulphite in an alum fixing bath, or a white scum of it on the material — a fault of too little acid rather than too much, with three named causes and one published removal.
• Insufficient solution volumeStage development, fixingLikely causes A spiral tank filled below the top of the film; A dish with too shallow a layer for the size of print; A volume scaled down without scaling the capacity down with itA tank or a dish with too little in it, which produces three different faults at once — a tide line where the solution ended, unevenness where it was shallow, and a bath exhausted before its published capacity.
• Over-fixingStage fixingLikely causes Fixing paper for the film time, which is two to five times too long; Leaving prints in the fixer while other work is finished; A rapid fixer at a film dilution used on paperThe fixer dissolving the picture as well as the halide — highlights first, because the deposits there are smallest, and paper first, because its published time is a fraction of film's.
• PinholesStage coating, exposure, stop, fixingLikely causes Gas evolved inside a soft layer where a carbonate developer met an acid bath; A bubble or a dust particle trapped in a hand-coated emulsion before it set; A dust particle lying on the plate at the moment of exposure, masking the lightOne name for three unrelated faults — a gas crater, a bubble in a hand-coated layer, and the shadow of a dust particle — told apart by their edges and by the company they keep.
• Reel and contact marksStage development, handlingLikely causes Film touching itself where a spiral was loaded badly or the reel was damp; Two turns of film pressed together on an over-filled reel; Sheets shuffled in a tray, pressed face to back so that solution is squeezed outBroad, soft, pale patches where two surfaces touched and no solution could get in — the fault of a badly loaded spiral or a shuffled stack, and how it differs from the crescent that force leaves behind.
• Repellency spotsStage coating, handlingLikely causes Grease from a bare finger on the support before coating; Silicone, aerosol overspray or hand cream on the support or in the air; A support cleaned with detergent that left a residueRound bare patches with a raised rim where the wet layer retreated from a low-energy contaminant, and the one observation that separates them from air bells.
• Residual thiosulfateStage washing, fixingLikely causes A wash too short, or one in which the water was not actually changing; A fibre-base paper washed as though it were resin-coated; Fixing carried far past the point needed, driving solution into the paper baseThiosulfate left in the layer after washing, invisible at the time, which supplies the sulfur that turns image silver into silver sulfide - and the silver nitrate test that finds it.
• ReticulationStage development, stop, fixing, washingLikely causes Solutions differing sharply in temperature, so the gelatin expands or contracts suddenly; A bath run at an extreme temperature; An unhardened or lightly hardened layer taken through a large temperature stepA coarse wrinkling all over the film from sudden swelling or contraction of the gelatin - a certain mechanism and a genuinely disputed reachability on modern materials.
• Room light leak, with a directionStage safelight, handling, storageLikely causes A gap around a door, a window, or a ventilator; A seam in the construction that is not opaque to visible light or to infrared; Light entering with a person, or from a device inside the roomFog that is heavier on one edge of the paper than the other - a leak has a direction, and the direction is what finds it.
• Safelight fogStage safelight, handlingLikely causes A safelight filter of the wrong class for the material being handled; Too long under the safelight, or too close to it; A material whose sensitivity extends into the colours the filter transmitsA uniform veil right to the cut edge of the sheet, present on the control that never went in the camera - and which often shows first as a loss of contrast rather than as visible fog.
• Silver mirroringStage storageLikely causes Oxidising gases from the atmosphere reaching the image silver; Poor-quality mount, mat or framing materials in contact with the print; Storage in an enclosure or climate that concentrates pollutants at the edgesA bluish metallic sheen starting at the edges and visible under reflected light, made by image silver that was oxidised, migrated to the surface and was reduced again there.
• Static discharge marksStage handling, exposure, equipmentLikely causes Rapid winding or rewinding of film in dry air, separating charge faster than it can leak away; Separating sheets or rolls quickly, especially interleaved sheet film; Low humidity in the space where film is handledBranch-like marks, spots with dark centres, or a row of dots — a photograph of an electrical spark, recorded by the film that made it, and told from a light leak by being sharp where a leak is graded.
• Thin coatStage coating, materialsLikely causes Too little emulsion laid down per unit area; A melt too dilute in gelatin to hold its thickness, often after noodle washing; A coating rod set closer to the sheet than the intended coating weight requiresA weak, low-contrast print that reads as a poor maximum black and is a coating fault - the trap that sends a coater back to change an emulsion that was never wrong.
• Under-fixingStage fixingLikely causes Fixing time shorter than twice the clearing time; A bath near exhaustion, so that silver leaves the grain as the sparingly soluble first complex; A thick or unevenly coated layer the fixer could not penetrateMilkiness or opalescence in the clear areas, which is the definition of the endpoint fixing did not reach - rescuable today, and invisible in its mild form until the third year.
• Uneven coating thicknessStage coatingLikely causes A bed that is not level, so the wet layer flows before it sets; Emulsion coated too warm, so it stays fluid long enough to flow; Too little gelatin for the volume, so the layer will not hold its thicknessA gradient with no edge to it - a heavier bottom, a heavier corner or a wedge - read for free in the fixing tray, because a plate clears last where it is thickest.
• Water spotsStage washing, dryingLikely causes Drops of water splashed onto a film that was already drying; Drops running from clips, from a shelf above, or from a neighbouring film; A wetting agent wrongly diluted, so that the rinse breaks into drops rather than sheeting offDiscrete round or teardrop marks where single drops sat and dried, distinguished from the streaks of a drainage fault by their shape — and from dirt by whether they appear dark or light by transmitted light.

Prints

• Age fogStage materials, storageLikely causes Time, which lets grains acquire developable centres without any exposure; Storage above the maker's recommended temperature, which accelerates it; High humidity in storageA raised floor on a film that was never exposed to anything — grains that became developable with time rather than with light, and the reason the first symptom is muddy shadows rather than a thin negative.
• Air bellsStage developmentLikely causes Air entrained when the developer was poured in, lodging against the emulsion; The tank not tapped on the bench after filling and at each agitation; A pour too slow or too turbulent, or a tank filled too farSmall, round, perfectly clear spots where a bubble sat against the emulsion and no developer reached it — and the one physical action both major manufacturers put in their published procedure to prevent them.
• Albumen crazing and yellowingStage storage, handling, fixing, washingLikely causes Variations in humidity, producing differential dimensional change between the albumen layer and the paper; Flexing, rolling or flattening a dry print, which cracks a shrunken layer; Residual fixer or atmospheric sulfur converting albumen-bound silver to silver sulfideA fine network of cracks across the surface and a yellow cast in the whites - one is an identification characteristic of the process and the other is its commonest deterioration.
• Base fogStage materials, storage, safelight, developmentLikely causes The material itself, from age, heat or over-ripening; A safelight, a light-tight box or a handling routine that is not light-tight; A developer that has gone over the alkali ladder or is contaminatedDensity where nothing was exposed, present on a control sheet that never went in the camera - the zero against which every other fault on a sheet is read.
• Bellows factor omittedStage exposure, equipmentLikely causes A frame added or removed to reframe, changing the focal distance and therefore the f-number; An exposure computed for one configuration and given in another; A configuration recorded in the log after the exposure rather than before itA thin negative because the frames were stacked to reframe and the exposure was not recomputed - the pinhole's version of the bellows factor, arriving as a changed f-number.
• Black spotsStage materials, coatingLikely causes Pepper, a coarse grain reduced to metallic silver without any exposure to light; Undissolved halide that developed out as a black slug; Rust or another metallic contaminant in contact with the silver solutionFine black dots through the image and through the unexposed areas too, sometimes invisible to the naked eye - pepper and slugs, which look alike and are not the same fault.
• Blistering from an over-hot hypo alum bathStage handling, fixingLikely causes A hypo alum bath run above 49 degrees Celsius; Toning for longer than twenty minutes at that temperature; A large temperature difference between the wash water and the toning bathSmall raised bubbles in the emulsion of a sepia-toned print - Kodak give the temperature above which they appear, and the toner is used at 49 degrees on purpose.
• BlistersStage stop, fixingLikely causes Carbon dioxide evolved when a carbonate-bearing developer meets an acid bath; A fixing bath carrying an excess of acid, together with insufficient rinsing before it; A strongly acid rinse bath used between developer and fixerGas evolved inside a soft gelatin layer, lifting it — a mechanism Kodak stated in 1928 and confirmed in 1944 by selling an alkali that avoids it, and which on dry film looks like a field of tiny craters in reflected light.
• Blocked highlightsStage exposure, developmentLikely causes Exposure that carried the brightest part of the subject past the top of the material's usable range; Development carried far enough to push the highlights onto the shoulder; A subject whose range exceeds what the material can hold, so no single exposure will fit itAn area that was bright in the subject and is now so dense that no detail can be seen in it - not recoverable, because the material stopped responding before the exposure ended.
• Bromide dragStage developmentLikely causes Reduced or absent agitation, letting spent developer sink from the dense areas; Long, dilute, nearly unagitated development, where the effect is the intended mechanism arriving as a fault; A tank or tray left standing between agitation cycles for too longStreaks running downward from the dense parts of a negative, made by spent developer that is denser than the bulk and sinks, retarding development in whatever it flows over.
• Bubbles and pinholes in a coatingStage coatingLikely causes Air whipped into the melt by stirring too vigorously or by shaking the bottle; Emulsion poured from a height rather than down the vessel wall; Air trapped under the layer as it was laid and never chased outClean round holes with no rim, made by air whipped into the melt or trapped under the layer as it was laid.
• Buckled-sheet softnessStage equipment, exposure, handlingLikely causes Insufficient pressure on the sheet in the back, so it bows towards the hole; Resin-coated paper from a freshly opened packet, which curls more than paper that has settled; A pressure plate with foam that has compressed with ageA denser centre, subtly bowed straight lines and a middle that is very slightly sharper - a density fault masquerading as a sharpness fault.
• Burr smearStage equipment, exposureLikely causes A lip of material pushed up on the far side when the plate was pierced; A hole finished from one side only, so the burr was never abraded off; A plate reworked after measurement, leaving a ragged flap in the light pathSoftness with a preferred direction that is the same at every point in the frame, from a lopsided aperture - and the one comparison that tells it from movement.
• Calcium scumStage washing, dryingLikely causes A hard water supply, whose dissolved calcium and magnesium are left behind as the last water evaporates; A final rinse made with tap water in a hard-water district; Too much wetting agent, which adds its own dissolved solid to what is left behindA whitish film left on a dried negative or print by hard water, and the two manufacturer answers that have not changed in eighty years — distilled water for the final rinse, and less wetting agent rather than more.
• Chemical fogStage developmentLikely causes Too much alkali, or a stronger alkali substituted for the one the formula names; Development carried far past the point where fog rises faster than image; A developer contaminated with something that raises its energyDensity on a patch that saw no light at all, produced by the developer rather than by the exposure - and which points up the alkali ladder rather than down it.
• Coating mottle and drying marksStage coating, dryingLikely causes A draught blowing directly on a drying sheet; A warm spot, or contact with the drying rack, drying part of the sheet faster than the rest; A change in the support the coater did not make, such as a paper whose sizing recipe was altered by its makerA soft irregular texture like a watermark, absent when the sheet was wet and present when it was dry, which is the whole of the diagnosis.
• CometsStage coating, materialsLikely causes Undissolved halide caught under the coating rod; A fragment of undissolved gelatin in the melt; A fibre or other solid picked up from the room or the vesselA dark or light head with a tail trailing behind it in the direction of the coating stroke, made by one solid particle caught under the rod.
• Cracked emulsion from flattening a bone-dry fibre printStage drying, handling, storageLikely causes Flattening or unrolling a print that has dried at low relative humidity; Drying too fast or too hot, which leaves the binder shrunken and stressed; Rolling a print for storage and unrolling it laterA network of fine cracks that appears when a curled fibre print is forced flat - gelatin that has shrunk at low humidity and lost the ability to bend.
• Developer contaminated by fixer or stopStage development, materialsLikely causes A graduate, funnel, stirrer or thermometer used for two baths without washing; Tongs moved between trays, or a hand that had been in the fixer; A bottle refilled from the wrong jug, or an unlabelled vesselTwo contaminations that arrive by the same route and behave nothing alike — a trace of thiosulfate, which the makers say to discard the bath over, and a splash of acid, which merely makes it slow.
• Developer fog on paperStage developmentLikely causes Development far beyond the recommended time, especially in a warm bath; A developer mixed too concentrated, or too alkaline; A print developer short of its bromide or organic restrainerGreyed whites that arrive with the developer rather than with the paper - too long, too warm, too alkaline, or short of the restrainer that was holding the unexposed grains back.
• Developer stainStage development, stop, handlingLikely causes Developer left on the material at a transfer, drying in air before it reached the stop bath; A sheet or a film only partly covered by the solution; Developer on a hand, a tong or a bench, transferred to dry paperA brown mark where developer was left on the material and oxidised in air — an edge, a drip, a fingerprint or a whole sheet — and the two observations that separate it from the stain a staining developer leaves on purpose.
• Dichroic fogStage development, fixingLikely causes Developer carried into the fixing bath without a rinse or a stop bath; An old, exhausted fixer already carrying an excess of dissolved silver; A silver-halide solvent in the developer meeting carried-over reducing agent inside the gelatinA veil that is greenish by reflected light and reddish-pink by transmitted light - finely divided metallic silver, which prolonged immersion in hypo does not mend.
• Diffraction glow from an undersized hole on paperStage equipment, exposureLikely causes A hole smaller than the optimum for the focal distance in use; A hole reduced below its band by abrading a burr off it; A plate chosen for a long focal distance and used at a short oneA soft glow spilling across every edge rather than a plain blur, because the hole is smaller than the optimum and the blur figure now has a bright core with far-reaching tails.
• Dilution ratio misread as a fractionStage materialsLikely causes A colon notation read as a ratio to the finished volume rather than to the water; A sheet writing 1+10 transcribed as 1 to 10 and then made up to ten parts; A formula copied from a secondary source that changed the notationA working solution about ten per cent out because a colon was read as a ratio to the total rather than as parts of stock to parts of water.
• Double image from a reflective plateStage equipment, exposureLikely causes A pinhole plate blackened on the outside face only; A bare metal plate used as made, with no blackening at all; A plate whose blackening has been abraded off the inside face by handlingA faint, broad, displaced ghost of the frame's own bright areas, thrown back by the unblackened inside face of the pinhole plate - described from the geometry, because the course has not photographed one.
• Dry-down errorStage drying, exposureLikely causes Judging a print wet and printing to that judgement; Inspecting under a bright light quite unlike the light the print will hang in; Applying a remembered fraction of a stop as a uniform correction to an effect that is not uniformA print that looked right wet and is too dark dry — a systematic error rather than a defect, which the course refuses to give a number for because no manufacturer publishes one and it is not the same at every density.
• Drying marksStage dryingLikely causes No wetting agent in the final rinse, so the film dries as drops rather than as a sheet; A wetting agent wrongly diluted — too little or too much; Hard water, which leaves more dissolved solid behindNot dirt on the gelatin but a change in it, left where the last of the water evaporated and everything dissolved in it stayed behind — with five causes, five published corrective actions, and an honest limit on what can be undone.
• Drying marks and squeegee lines on printsStage washing, drying, handlingLikely causes A squeegee blade with a nick, or grit trapped under it; Wiping a print that has not been washed clean, so the blade spreads residue; Uneven drying, so a boundary between wet and dry areas dries at a different rateStraight lines and tide marks left by the tool or the water rather than by the picture - a surface fault that lands on the one part of a print the eye checks first.
• Edge fading from mount and adhesiveStage storage, handlingLikely causes A mounting board with a lignin-rich core, whose decomposition products migrate through the top layer; A mounting adhesive that has decomposed, such as a putrefied starch or gelatin paste; A mat, window or frame backing in contact with the print, releasing oxidising or acidic productsA print that faded in a band around its edges, or under a mat, while the covered oval stayed clean - the mount is part of the chemistry, and lignin is the usual culprit.
• Edge leakStage equipment, exposure, handlingLikely causes Light entering at a body seam or corner and spreading inside the camera; The mouth of the dark-slide slot admitting light around the slide; A joint that runs the length of an edge and was never light-trappedA broad soft band along one edge of the sheet, densest at the edge and fading inwards, which continues under the strips the paper stops covered.
• Empty shadowsStage exposure, developmentLikely causes Underexposure, so the darkest parts of the subject never made a developable centre; A reciprocity correction omitted or taken from the wrong material; A subject whose range exceeds what the material can holdAn area that was dark in the subject and is now indistinguishable from clear film base, with nothing in it - the unrecoverable failure at the other end of the scale.
• Emulsion-side scratchesStage development, washing, drying, handlingLikely causes A squeegee or chamois with grit caught in it; Contact with a rough surface while the emulsion was swollen and soft; Dirt or chemical build-up on rollers, racks or squeegees in a processorA groove cut into the layer that carries the picture, so silver has actually been removed — which is why it prints black, why no fluid will hide it, and why it convicts the wet side of the process.
• Enlarger lamphouse or bellows leakStage equipment, safelight, exposureLikely causes A gap or a vent in the lamphouse that is not baffled; A pinhole or a split in the bellows; A negative carrier that does not mask the whole apertureFog that appears only while the enlarger is on, strongest near the column - light escaping from the head rather than reaching the paper through the lens.
• Exhausted developerStage development, materialsLikely causes More film or paper put through the bath than its published capacity allows; No time compensation applied as the running total rose; A working solution reused past the point where its by-products restrain itA thin, flat strip with a fog floor lower than the control's - the one discriminator that separates a bath that has done too much work from a bath that has merely oxidised.
• Exhausted fixerStage fixingLikely causes More material put through the bath than its published capacity allows; No clearing-time test on a schedule, so the bath was judged by appearance; Developer carried in without a rinse or a stop bath, spending the acid and the sulfite reserveA bath whose clearing time has doubled, whose curve is flat for two thirds of its life, and which fails by leaving something invisible behind rather than by refusing to work.
• Fingerprints on paperStage handling, development, fixingLikely causes A hand that had been in the fixer touching unexposed or undeveloped paper; A hand that had been in the developer touching dry paper; Handling wet prints by the surface rather than by the edgeA print of the ridges of a finger, made of chemistry rather than grease — white if the hand had been in the fixer, dark if it had been in the developer, and permanent either way.
• Fixer contaminated by developerStage fixing, stopLikely causes No stop bath and no rinse between developer and fixer; A water rinse used too many times without being changed; Prints, which carry far more developer than film doesThe one contamination that happens on every film you process — the question is only how much — and the three separate faults that carried-over alkaline developer produces in an acid bath.
• Flare veilStage equipment, exposureLikely causes A shiny or light-coloured camera interior returning light that missed the film; An unblackened pinhole plate reflecting light back onto the sheet; A bright source just outside the frame, striking the interior walls at a shallow angleCorrect overall density with flat grey shadows and clean highlights, from light that came through the hole and bounced off the interior - and which stops dead at the paper stops.
• FrillingStage development, fixing, washing, coatingLikely causes Adhesion failure at the emulsion-support interface, worst at a free edge; Baths differing in temperature, or a bath run warm; A support that was contaminated, unsubbed or inadequately cleanedThe layer lifting, rolling back or detaching at the edges during processing, and the sourced remedy that is a hardening fixer rather than a hardener in the emulsion.
• Geometric softness from an oversized holeStage equipment, exposureLikely causes A hole larger than the optimum for the focal distance in use; A plate chosen for a short focal distance and used at a long one; A hole enlarged by piercing further than intended and never re-measuredPlain, even, flat-topped blur across the whole frame, the same in every direction, because the hole is larger than the optimum for the focal distance it is being used at.
• Grey highlights from developer exhaustion, as distinct from fogStage developmentLikely causes A print developer worked past its published capacity; A bath left standing in an open dish between sessions; A developer diluted further than the recommended working strengthA print that will not go white and will not go black, made in a bath that has done its work - and the unexposed sheet that tells exhaustion from fog in one test.
• Hardener sludgeStage fixingLikely causes Too little acid in the hardener, or the wrong strength of acid used in mixing; Developer carried over into the bath, neutralising the acid that was there; A bath exhausted, still carrying alum and sulphite but no acidA white gelatinous precipitate of aluminium sulphite in an alum fixing bath, or a white scum of it on the material — a fault of too little acid rather than too much, with three named causes and one published removal.
• Heat fogStage materials, storageLikely causes Storage above the maker's stated temperature, briefly or for a season; A film left in a hot vehicle, a loft, a conservatory or beside a radiator; High humidity together with heat, which the makers name as a pairThe same fault as age fog, arriving in an afternoon instead of a decade — and the reason a glovebox in summer is worse for a film than a year in a cupboard.
• Hot spotStage equipment, exposureLikely causes A bright, flat interior wall reflecting specularly rather than diffusely; A source just outside the frame striking that wall at a shallow angle; An interior finish that is matt to the eye and glossy at grazing incidenceA bright patch on the negative near one edge, roughly the shape of the interior wall it reflected from and always on the side away from the source - described here from the geometry, because the course has not photographed one.
• Hydrate substituted for an anhydrous salt at the same massStage materialsLikely causes The jar on the shelf is a different hydrate from the one the formula names; A pre-1950 formula whose unqualified names mean the crystallised forms; A formula that names a salt without stating its hydrate state at allA developer 2.7 times too alkaline, or a fixer well under strength, because water of crystallisation was weighed as though it were the salt.
• Hypo spots on unexposed paperStage handling, materialsLikely causes A splash of fixer reaching the paper box, the easel or the dry bench; A hand that had been in the fixer touching unexposed paper; Wet fingers or tongs handling paper on the dry sideWhite marks that no exposure can fill, because the silver halide under them was dissolved before the enlarger was ever switched on — a bench fault rather than a bath fault, and completely unrecoverable.
• Insufficient solution volumeStage development, fixingLikely causes A spiral tank filled below the top of the film; A dish with too shallow a layer for the size of print; A volume scaled down without scaling the capacity down with itA tank or a dish with too little in it, which produces three different faults at once — a tide line where the solution ended, unevenness where it was shallow, and a bath exhausted before its published capacity.
• Lamp glowing faintly between exposures, from a switching device that leaksStage exposure, safelight, equipmentLikely causes A solid-state switched output passing its rated off-state current through the lamp; A faulty switching device passing far more than its rated off-state current; A load that is not a tungsten filament responding to a few milliampsAn enlarger lamp that never goes fully dark between exposures, from a switched output that leaks when it is commanded off - what it can and cannot do to paper, and why the test is a sheet of paper rather than a meter.
• Light-leak fogStage equipment, handling, storageLikely causes A leak in the camera body, the shutter or the dark slide; A film or paper box that is not light-tight; A loading routine carried out where light could reach the materialFog that came in through a hole rather than through the picture - identified by whether it crosses the parts of the sheet the picture could never reach.
• Motion smearStage exposure, handlingLikely causes The camera moved, from wind on the tripod or a knock; The subject moved, which on an exposure of minutes is normal for leaves, water, cloud and people; The shutter jarred the camera at one end of the exposureThe one kind of unsharpness that cares which way an edge runs - and the single loupe comparison that separates every movement fault from every optical one.
• Mottle revealed only after toningStage stop, developmentLikely causes An over-concentrated stop bath, usually from evaporation in a standing tray; Insufficient agitation in the first few seconds in the stop bath; Uneven development that the untoned print did not showA print that was even until it went into the toner - Kodak name the cause exactly, and it is the stop bath rather than the toner.
• Mottled developmentStage developmentLikely causes Inadequate agitation, so that depletion patterns survive across the frame; A semi-stand or reduced-agitation regime taken further than the material tolerates; Solution volume too small for the surface being developedAreas of non-uniform density with no direction to them, which manufacturers put squarely against inadequate agitation - the opposite end of the same lever from surge marks.
• Muddy print from a snatched developmentStage development, exposureLikely causes Removing the print when the image looks right rather than at the recommended time; Over-exposure compensated by a short development, which is the commonest route into it; A developer too warm, so the image arrives before development is completeA print pulled from the developer when it looked right, which dries flat, grey and slightly uneven - the fault of judging a print by the moment the image arrives rather than by the time it needs.
• Near-limit softnessStage exposureLikely causes The nearest subject sitting closer than the configuration's near limit; A near limit never computed for the focal distance in use; A still life or portrait framed at a distance chosen for composition aloneOne object soft with everything behind it as sharp as the camera ever gets, because the blur circle grows as the subject comes closer and a pinhole has no focus to lose.
• Negative poppingStage equipment, exposure, handlingLikely causes A glassless carrier at a high magnification, where the film is gripped at its edges and has nowhere to expand but out of the plane; A negative put in the carrier cold, focused at once, and exposed while it is still warming to the lamphouse's temperature; A tungsten head, whose filament emits far more infrared than visible light and sends almost all of it through the negativeA print whose fine detail is present but weak, veiled at hard edges and faintly doubled, in a band that lands somewhere different on every sheet - the negative moving in the heat of the beam part way through the exposure, and the one test that changes only its temperature.
• Newton's ringsStage equipment, exposure, handlingLikely causes A glass negative carrier whose plain glass comes within a wavelength of the smooth film base over part of the frame; A contact printing frame closed hard enough, or backed softly enough, that the base and the glass reach near-perfect contact across a wide area; Anti-Newton glass fitted with its textured face away from the film, so the texture prints and the fringes form anywayClosed, irregular grey loops on the print, like contour lines, that were never on the negative - the fault that forms where contact between film and glass is almost perfect, and the one test that separates it from a stain.
• One soft corner from misalignmentStage equipment, exposureLikely causes The negative stage not parallel to the lens board - a carrier that does not seat, or grit under its rebate; The lens board not parallel - a burr, a squashed washer, or a lens that does not sit square on the board; The easel or baseboard not parallel - a warped board, a dried splash underneath, or an easel that holds the paper proud on one edgeOne corner of the print blurred while the diagonally opposite corner is as sharp as the centre - the asymmetry that separates a tilted plane from a lens, a lifted negative and a missed focus, and the one-variable test that settles it on a single sheet.
• Over-fixingStage fixingLikely causes Fixing paper for the film time, which is two to five times too long; Leaving prints in the fixer while other work is finished; A rapid fixer at a film dilution used on paperThe fixer dissolving the picture as well as the halide — highlights first, because the deposits there are smallest, and paper first, because its published time is a fraction of film's.
• Oxidation stainStage development, stop, fixingLikely causes Material moved from developer to fixer with little or no rinsing; A fixer whose sulfite has been used up and whose acid has been neutralised; Developer allowed to oxidise on the surface of the material before it reached the next bathA brown or yellow-brown general stain present from the first day, from developer carried into a fixer with too little sulfite and acid left to deal with it.
• Oxidised developerStage storage, materials, developmentLikely causes A bottle stored with a large headspace, so that every opening presented a fresh air interface; A stock kept beyond its published storage life; A tray or open tank left standingAn amber or brown solution that gives a thin, flat negative with a normal fog floor - and the asymmetry that matters, which is that colour convicts and clear does not acquit.
• Paper storage fogStage storage, materialsLikely causes Storage warm, damp, or both, over months; Age beyond the material's stated keeping life; A box opened in the light, or stored where light reaches the packetGrey highlights and a lifted base on paper that was never mishandled in the darkroom - the fault arrived with the box, from heat, damp, age or a stray exposure in store.
• Poor maximum blackStage development, fixing, safelight, materials, exposureLikely causes A print developer exhausted, too cold, too dilute, or the wrong time for the dilution; Development cut short, before the deepest tones had finished building; Fog on the base from the safelight or the room, which destroys the difference rather than the blackA print whose steps stop getting darker before they reach black — the ceiling has moved, and there are seven places it can have moved from, in a check order that eliminates the cheap ones first.
• Print mottleStage developmentLikely causes Too little developer in the dish for the size of print; Agitation too gentle, or a rocking rhythm that never changes direction; A developer near the end of its capacity, especially under large dark areasA soft patchiness inside a tone that should be even — the film fault in a dish, invisible on a test strip, and quantified by the manufacturer's capacity table rather than by the clock.
• RC blistersStage stop, fixing, dryingLikely causes Carbon dioxide evolved when a carbonate-bearing print developer meets an acid bath; A fixing bath carrying an excess of acid, together with insufficient rinsing before it; A soft or over-swollen emulsion, from an over-alkaline developer or from warm workingA raised bubble between the polyethylene skins of a resin-coated print, whose established mechanism is gas from a carbonate developer meeting an acid bath — and whose popular attribution to drying heat the course cannot support.
• Reel and contact marksStage development, handlingLikely causes Film touching itself where a spiral was loaded badly or the reel was damp; Two turns of film pressed together on an over-filled reel; Sheets shuffled in a tray, pressed face to back so that solution is squeezed outBroad, soft, pale patches where two surfaces touched and no solution could get in — the fault of a badly loaded spiral or a shuffled stack, and how it differs from the crescent that force leaves behind.
• Repellency spotsStage coating, handlingLikely causes Grease from a bare finger on the support before coating; Silicone, aerosol overspray or hand cream on the support or in the air; A support cleaned with detergent that left a residueRound bare patches with a raised rim where the wet layer retreated from a low-energy contaminant, and the one observation that separates them from air bells.
• Residual silver and yellow stainingStage fixing, washing, storageLikely causes An exhausted fixer leaving the sparingly soluble first silver-thiosulfate complex in the paper; Fixing time too short for the material and the bath; A single fixing bath used where two were neededA yellowing that was not there when the print dried, strongest in the borders and highlights - the retained complex sulfiding, and the geography of the stain is a map of where the halide was.
• Residual thiosulfateStage washing, fixingLikely causes A wash too short, or one in which the water was not actually changing; A fibre-base paper washed as though it were resin-coated; Fixing carried far past the point needed, driving solution into the paper baseThiosulfate left in the layer after washing, invisible at the time, which supplies the sulfur that turns image silver into silver sulfide - and the silver nitrate test that finds it.
• ReticulationStage development, stop, fixing, washingLikely causes Solutions differing sharply in temperature, so the gelatin expands or contracts suddenly; A bath run at an extreme temperature; An unhardened or lightly hardened layer taken through a large temperature stepA coarse wrinkling all over the film from sudden swelling or contraction of the gelatin - a certain mechanism and a genuinely disputed reachability on modern materials.
• Room light leak, with a directionStage safelight, handling, storageLikely causes A gap around a door, a window, or a ventilator; A seam in the construction that is not opaque to visible light or to infrared; Light entering with a person, or from a device inside the roomFog that is heavier on one edge of the paper than the other - a leak has a direction, and the direction is what finds it.
• Round purple spots from air bubbles trapped in the fixerStage fixing, handlingLikely causes Air bubbles trapped between or under prints during fixing; Prints sticking together, or floating on the surface of the fixer; Too many prints in the tray for the agitation being givenCircular purple marks that appear only after selenium or sulfide toning - Kodak trace them to air trapped between or under prints during fixing, which is a handling fault with a delayed verdict.
• Safelight fogStage safelight, handlingLikely causes A safelight filter of the wrong class for the material being handled; Too long under the safelight, or too close to it; A material whose sensitivity extends into the colours the filter transmitsA uniform veil right to the cut edge of the sheet, present on the control that never went in the camera - and which often shows first as a loss of contrast rather than as visible fog.
• Safelight-fogged control stripStage safelight, handlingLikely causes A safelight filter that is wrong, faded or cracked for the material in use; Too high a bulb wattage, too short a distance, or too many safelights; Handling time longer than the material's safe time under that illuminationA control strip whose D-min has risen and whose highlights have closed up, with speed and contrast almost untouched - the sensitometric signature of light that was supposed to be safe.
• Seam leakStage equipment, exposureLikely causes An unfilled screw hole giving a straight path from outside to the film; A crack or split in the body; A gap at a rebate where two panels meet without an overlapA sharp streak or wedge running in from a corner, which is a straight optical path - a screw hole, a crack or a gap at a rebate - rather than light spreading from an edge.
• Session exposure driftStage exposure, development, equipmentLikely causes A light source still warming, whose output falls as its junction or filament temperature rises; Supply variation, or a lamp fed from a circuit doing other work; A print developer exhausting on the work it has donePrints that get darker or lighter through an evening at the same nominal exposure - a lamp warming, a supply sagging, or a developer working itself out, and one test that tells the three apart.
• Shutter leakStage equipment, exposureLikely causes A sliding blade lying flat against the outside of the front panel rather than running in a rebated channel; A wedge-shaped gap at the blade edge that admits light at shallow angles; A shutter that was not fully closed between exposuresA band of raised density along the edge nearest the shutter, present on the capped-pinhole sheet and absent on the closed-shutter sheet, which is what identifies it and nothing else does.
• Silver mirroringStage storageLikely causes Oxidising gases from the atmosphere reaching the image silver; Poor-quality mount, mat or framing materials in contact with the print; Storage in an enclosure or climate that concentrates pollutants at the edgesA bluish metallic sheen starting at the edges and visible under reflected light, made by image silver that was oxidised, migrated to the surface and was reduced again there.
• Silver mirroring and sulfiding in an untoned printed-out printStage storage, washing, fixingLikely causes An untoned image of colloidal silver, unprotected by conversion to a more stable compound; Residual thiosulfate and silver-thiosulfate complexes from inadequate fixing and washing; Oxidising gases in the atmosphere, or in the framing and mounting materialsA metallic sheen by reflected light and a general loss of image by transmitted light - two different attacks on the same very finely divided silver, and toning is the answer to both.
• The gold toner that did nothing because the first wash was omittedStage washing, handlingLikely causes The pre-toning rinse omitted, so excess silver went into the toning bath with the print; A gold bath already spent, because each print consumes gold from it; A dry print put into the toner without soaking, so the toner never reached the imageA print that sat in an expensive bath and came out the colour it went in - the two-minute rinse before the toner is not a formality.
• The printed-out image that bleached away in the fixerStage fixingLikely causes A fixing bath too strong, too long, or of the wrong kind for an unprotected silver image; Toning after fixing rather than before it, so the image met the hypo unprotected; Under-exposure, on a process that must be over-printed to survive processingA rich purple print that went pale and thin in the hypo - the fixer dissolving the image as well as the unexposed salt, and the two ways of stopping it.
• Thick-plate vignettingStage equipment, exposureLikely causes A pinhole plate thicker than about one fifth of the hole diameter; A hole drilled rather than pierced, leaving a parallel-sided bore; Steel shim used because it was what was in the drawerDark edges and corners with a comparatively hard boundary at a computable radius, because a hole in a thick plate is a short tunnel and beyond a certain angle no light passes at all.
• Thin coatStage coating, materialsLikely causes Too little emulsion laid down per unit area; A melt too dilute in gelatin to hold its thickness, often after noodle washing; A coating rod set closer to the sheet than the intended coating weight requiresA weak, low-contrast print that reads as a poor maximum black and is a coating fault - the trap that sends a coater back to change an emulsion that was never wrong.
• Timer display fogStage safelight, handlingLikely causes A timer, thermometer or exposure monitor with a lighted display facing the working surface; An indicator lamp on a power strip, a heater or a charger; A display bright enough at a wavelength the paper still responds toA faint patch of fog the shape of whatever was on the bench facing the paper - a lighted dial is a light source, and Kodak name it as one.
• Toner penetration at the edges of an RC printStage handling, washingLikely causes Toning a resin-coated print for longer than the recommended few minutes; Cut edges, which expose the paper core between the two resin layers; Insufficient washing after toning, which cannot reach what has entered the coreA dark or discoloured border creeping in from the cut edges of a resin-coated print - toner that got into the paper core through the one place the resin does not cover.
• Tong marksStage development, fixing, handlingLikely causes A tong used in more than one tray, carrying fixer or stop into the developer at the point of contact; Pressure on a soft wet emulsion at the grip point; A tong gripping inside the image area rather than at the very edgeSmall paired marks at the grip point, which are either a chemistry mark or a pressure mark depending on what the tong had been in — and the direction of the density change says which.
• Under-fixingStage fixingLikely causes Fixing time shorter than twice the clearing time; A bath near exhaustion, so that silver leaves the grain as the sparingly soluble first complex; A thick or unevenly coated layer the fixer could not penetrateMilkiness or opalescence in the clear areas, which is the definition of the endpoint fixing did not reach - rescuable today, and invisible in its mild form until the third year.
• Uneven coating thicknessStage coatingLikely causes A bed that is not level, so the wet layer flows before it sets; Emulsion coated too warm, so it stays fluid long enough to flow; Too little gelatin for the volume, so the layer will not hold its thicknessA gradient with no edge to it - a heavier bottom, a heavier corner or a wedge - read for free in the fixing tray, because a plate clears last where it is thickest.
• Uneven contact print from pressure, glass or source geometryStage equipment, exposure, handlingLikely causes Non-uniform pressure in the frame, so the gap between the two emulsions is not zero everywhere; Curl, grit, a bowed back or foam that has taken a set, holding the sandwich open in one region; Glass too thin to resist bowing, not flat, or carrying an anti-Newton texture that printsA proof sheet with dark corners, a regular stripe, or soft patches in an otherwise sharp frame - three unrelated faults sharing one complaint, separated by taking the negative out and printing the light on its own.
• Uneven enlargement from mixing chamber, alignment, lens falloff or mechanical vignetteStage equipment, exposureLikely causes A light source or mixing chamber that does not illuminate the negative evenly; Enlarger misalignment, so one part of the paper is further from the lens than another; Lens illumination falloff, which is a property of every lens and worst wide openA print brighter in the middle than at the corners, or brighter on one side than the other - four causes with four different patterns, and a measurement that separates them.
• Uneven f-stop test-strip bandsStage exposure, development, equipmentLikely causes Enlarger illumination falling off across the strip, so the bands sample different places on the baseboard; A cumulative strip in which the card was moved late, early or by the wrong amount; Increments rounded one at a time, so each band inherits every earlier roundingA test strip whose bands do not step evenly in tone even though the timer was given an f-stop series - the four causes, and why only one of them is the timer's fault.
• Uneven print developmentStage developmentLikely causes Too little developer in the dish, so the local reservoir is the whole reservoir; A rocking rhythm that never changes direction, setting up a standing flow pattern; A developer near the end of its capacity, especially under a large dark areaA large sheet that develops unequally across its area — the film mechanism in a dish, quantified by the manufacturer's own capacity table, and prevented by volume and by a rocking motion that changes direction.
• Uneven toningStage fixing, washing, development, handlingLikely causes Residual silver salts and traces of hypo left by inadequate fixing or washing; A hardening fixer, which makes the emulsion less receptive to the toner; A dry print put into the toner without soaking, or a print entered slowlyA print that toned in patches rather than as a whole - and a list of causes that is almost entirely about what happened before the toner.
• Water spotsStage washing, dryingLikely causes Drops of water splashed onto a film that was already drying; Drops running from clips, from a shelf above, or from a neighbouring film; A wetting agent wrongly diluted, so that the rinse breaks into drops rather than sheeting offDiscrete round or teardrop marks where single drops sat and dried, distinguished from the streaks of a drainage fault by their shape — and from dirt by whether they appear dark or light by transmitted light.
• Weak or grey blacksStage safelight, development, exposure, materialsLikely causes Fog on the paper base, from the safelight, the room or the enlarger, which raises everything from below; Underexposure, so the tones that should be black were never given enough light; A print developer that is exhausted, cold or diluteA print with no true black anywhere, which reads as flat at every grade — usually a raised base rather than a lowered ceiling, and the border tells you which in one look.
• Yellow-brown highlight stain from residual silverStage fixing, washing, storageLikely causes Silver bound to the binder in non-image areas, which fixing does not remove; Residual fixer decomposing and supplying sulfur to that bound silver; Atmospheric sulfur compounds reaching the print in storageWhites that went yellow while the image stayed put - silver bound so tightly to the binder that hypo cannot reach it, and a stain that no known treatment removes.

Solutions and baths

• Control chart: contaminationStage development, handlingLikely causes Fixer or stop bath carried into the developer on hands, tongs or a shared vessel; Mixing equipment that was not thoroughly cleaned between solutions; Dry chemical made airborne during mixing and settling into an adjacent solutionA chart that moves in a way none of the other signatures explains - and an entry that states, rather than fills, the gap where a measured figure ought to be.
• Cross-contamination between alternative processes sharing a benchStage coating, development, handling, materialsLikely causes A brush, rod, pipette or tray used for more than one process; Two sensitisers mixed, deliberately or by residue, whose ions are incompatible; The developer of one process used on the print of anotherBlue where there should be brown, white spots where there should be tone, and a developer that bleaches the wrong image - the faults of running several iron processes in one room.
• Developer contaminated by fixer or stopStage development, materialsLikely causes A graduate, funnel, stirrer or thermometer used for two baths without washing; Tongs moved between trays, or a hand that had been in the fixer; A bottle refilled from the wrong jug, or an unlabelled vesselTwo contaminations that arrive by the same route and behave nothing alike — a trace of thiosulfate, which the makers say to discard the bath over, and a splash of acid, which merely makes it slow.
• Dilution ratio misread as a fractionStage materialsLikely causes A colon notation read as a ratio to the finished volume rather than to the water; A sheet writing 1+10 transcribed as 1 to 10 and then made up to ten parts; A formula copied from a secondary source that changed the notationA working solution about ten per cent out because a colon was read as a ratio to the total rather than as parts of stock to parts of water.
• Exhausted developerStage development, materialsLikely causes More film or paper put through the bath than its published capacity allows; No time compensation applied as the running total rose; A working solution reused past the point where its by-products restrain itA thin, flat strip with a fog floor lower than the control's - the one discriminator that separates a bath that has done too much work from a bath that has merely oxidised.
• Exhausted fixerStage fixingLikely causes More material put through the bath than its published capacity allows; No clearing-time test on a schedule, so the bath was judged by appearance; Developer carried in without a rinse or a stop bath, spending the acid and the sulfite reserveA bath whose clearing time has doubled, whose curve is flat for two thirds of its life, and which fails by leaving something invisible behind rather than by refusing to work.
• Fixer contaminated by developerStage fixing, stopLikely causes No stop bath and no rinse between developer and fixer; A water rinse used too many times without being changed; Prints, which carry far more developer than film doesThe one contamination that happens on every film you process — the question is only how much — and the three separate faults that carried-over alkaline developer produces in an acid bath.
• Grey highlights from developer exhaustion, as distinct from fogStage developmentLikely causes A print developer worked past its published capacity; A bath left standing in an open dish between sessions; A developer diluted further than the recommended working strengthA print that will not go white and will not go black, made in a bath that has done its work - and the unexposed sheet that tells exhaustion from fog in one test.
• Hardener sludgeStage fixingLikely causes Too little acid in the hardener, or the wrong strength of acid used in mixing; Developer carried over into the bath, neutralising the acid that was there; A bath exhausted, still carrying alum and sulphite but no acidA white gelatinous precipitate of aluminium sulphite in an alum fixing bath, or a white scum of it on the material — a fault of too little acid rather than too much, with three named causes and one published removal.
• Hydrate substituted for an anhydrous salt at the same massStage materialsLikely causes The jar on the shelf is a different hydrate from the one the formula names; A pre-1950 formula whose unqualified names mean the crystallised forms; A formula that names a salt without stating its hydrate state at allA developer 2.7 times too alkaline, or a fixer well under strength, because water of crystallisation was weighed as though it were the salt.
• Oxidised developerStage storage, materials, developmentLikely causes A bottle stored with a large headspace, so that every opening presented a fresh air interface; A stock kept beyond its published storage life; A tray or open tank left standingAn amber or brown solution that gives a thin, flat negative with a normal fog floor - and the asymmetry that matters, which is that colour convicts and clear does not acquit.
• Precipitate in a stock solutionStage materials, development, fixing, storageLikely causes Metol precipitated by a strong sulfite solution during mixing, which usually redissolves; Aluminium sulphite in an alum fixing bath whose acid has been neutralised; Sulphur in an acid fixing bath with too much acid, too little sulphite, or run warmSomething has come out of a made-up bath — and whether that matters depends entirely on what it is, which its colour and its behaviour on warming will tell you in five minutes.
• Sensitiser gone cloudy in the bottleStage storage, materialsLikely causes A sparingly soluble salt crystallising out of a mixed sensitiser; Mould growing on a citrate solution, which is an excellent nutrient medium; An expected precipitate that the process's own instructions describe and tolerateA stock that was clear and is not - and four different clouds, only two of which mean the bottle should be thrown away.
• Solution made by adding solid to a litre rather than making up to a litreStage materialsLikely causes "Water to 1 litre" read as a description of how much water to measure out rather than as an instruction; A litre measured first and the solid tipped into it; Water of crystallisation from a hydrate adding volume nobody countedThe commonest mixing error in the whole course - a solution weaker than the formula says because the dissolved solid took up volume of its own.
• Stock solution crystallised in cold storageStage storage, materialsLikely causes A concentrated stock stored below the temperature at which its most soluble constituent stays in solution; An unheated garage, shed or outbuilding used as chemical storage; A stock mixed close to saturation and then cooledCrystals in the bottom of a concentrated stock kept too cold, and the reason the clear liquid above them is not the stock you made.
• Undissolved chemicalStage materialsLikely causes Water too cold for the constituent being dissolved; The next chemical added before the previous one had fully dissolved; Insufficient stirring, or powder tipped in as a mass so that it cakedSolid still at the bottom of a bath that was supposed to be a solution — which is sometimes exactly what the maker says to expect, and sometimes a formula you have not actually made.
• Unlabelled or undated containerStage materials, storageLikely causes The bottle was filled first and labelled "in a minute"; A decant that inherited none of the supplier label it came from; A label carrying a family abbreviation only, with no substance, strength or dateA bottle whose contents cannot be stated is not a chemical but an unknown, and the fault is on the outside of the glass rather than in the liquid.