Break/Fix: The Room That Fogs and the Light That Is Not Even

The situation

It is October and you are printing in the room you commissioned in July. Nothing has been moved, nothing has been bought, and the last session before the summer went perfectly.

Tonight, every print comes out of the fixer looking tired. The whites are not white — they carry a faint even grey that you notice only when you lay a print next to one from July. The blacks are not quite black either; they look like the deepest tone of a print that has been left a moment too long in the light. And on top of all that, every contact print is lighter in one corner — the same corner every time, a smooth fall of tone across perhaps a third of the sheet, with nothing in the negative to explain it.

Two faults, or one? You do not know yet, and the temptation is to change something — a fresher developer, a harder grade, a longer exposure — and see what happens. Every one of those changes destroys evidence.

This page is a session of about seventy-five minutes that finds out what is wrong with the room and the equipment, and it is honest at the outset about what it does not cover: if the fault turns out to be in the developer, the fixer, the paper or the technique, this page hands it on rather than guessing at it. The hand-off is stated in Where this page stops, and reading it first is not cheating.

Before you start

Level A, and it is the ordinary print sequence: gloves, eye protection, ventilation, three marked dishes with one pair of tongs each, spent fixer and first wash collected as silver-bearing waste with local regulation governing disposal. Nothing is weighed and no concentrate is decanted.

The one hazard peculiar to this session is that it involves switching lights on and off repeatedly in a dark room with liquids in it. Clear the floor before the lights go off, put the trays in a fixed order that will not change, and decide before you start where the white-light switch is by touch. No electrical work is performed on this page at all.

Alternative route

Without a densitometer, everything here works. The differential is built on patterns — where the fog is, which way the gradient runs, whether an edge is clean — rather than on magnitudes, and every one of those is a visual judgement made against a control sheet lying beside the test sheet in even light. What you lose is the ability to say how much, which matters for the record rather than for the diagnosis. Write down which test you did.

Without an enlarger, roughly two thirds of the page is yours. Every fog row applies unchanged, since fog does not care what exposed the paper. Of the unevenness rows, the light box, the contact pressure and the development rows are yours and the lens, alignment and carrier rows are not — which is worth noticing, because it means a contact printer has four fewer ways to go uneven and is correspondingly easier to diagnose.

Without a permanent darkroom, the evidence list still works but it costs more care. A temporary blackout is a configuration that is rebuilt every session, so a leak that was not there last month is far more likely, and the leak test genuinely does have to be re-run rather than looked up. Treat “the leak-test record and its date” in the evidence list as “the leak test you ran when you last put this blackout up”, and if that was three sessions ago, run it again tonight — it is the cheapest item on the list.

Without a fresh unopened packet of paper, the second control in the evidence list is unavailable and the differential loses its floor. There is no substitute for it and the page will not pretend there is: a single sheet from a friend, a half-packet from a different box, anything from a different batch will do, provided you write down what it was. What you cannot do is skip the control and reason as though you had it.

The symptoms

Fog, flare and development faults look different from each other, and describing what you actually see is most of the diagnosis. Do this in even daylight, with the prints dry, laid beside a print from July.

Six fault signatures, and the two this page hands on

1. 1Safelight fog — even grey to the sheet edge, border included; grows with handling time
2. 2Room leak — even grey with a direction; heavier on one edge
3. 3Lamphouse or bellows leak — picture area veiled, border under the blades clean
4. 4Indicator or display fog — a local patch shaped like whatever faced the paper
5. 5Paper age or storage fog — identical to 1 by inspection; only a fresh packet separates them
6. 6Mechanical vignette — no fog; a hard-edged corner that ignores the aperture
7. 7Developer age, dilution, temperature or contamination — PART XVIII: clean whites, dull blacks
8. 8Fixing or washing fault — PART XVIII and XII: a stain, not a veil

Border first, then direction, then the edges of the affected area. Panels 5 and 1 are deliberately drawn the same, because they look the same and are told apart by a control rather than by looking harder.

Four questions, asked in this order, and each one has a wrong answer that costs you an hour.

1. Is the white border under the easel blades grey, or is it clean? This is the single most informative observation on the page. The blades masked that strip from everything arriving through the lens, and from nothing else. Grey border: the fog came from the room, the safelight, an indicator or the paper. Clean border with a veiled picture area: it came down the lens path, which means the lamphouse, the bellows, or flare.

2. Is the grey even, or does it run? An even veil across the whole sheet is a source that reached every part of the paper equally, which is a safelight, an overhead leak or the paper itself. A veil that is heavier on one edge has a direction, and a direction points at a hole.

3. Is it a veil or a patch? A soft-edged patch of grey the size of your hand, near one edge of the sheet, is a local emitter: Kodak name lighted dials on equipment controls explicitly among the things that fog paper, and a modern timer with an LED display is exactly that.

4. Are the whites veiled, or are the blacks dull, or both? Fog lifts the whites first and the blacks last. Dull blacks with clean whites is a different fault and it is not this page’s — see Where this page stops.

Evidence to collect

Before you touch anything. Six items, and four of them cost nothing.

Evidence	How to get it	What it establishes
Control 1: an unexposed sheet from the packet you are printing from	In the dark, take a sheet, put it straight into the developer, and process it normally with nothing else in the tray	The base plus fog of the paper you are actually using, including anything that has happened to it in your darkroom
Control 2: an unexposed sheet from a fresh, unopened packet	Open a new packet in the dark, take one sheet, process it the same way	The paper’s base plus fog before your room touched it. The difference between the two controls is the whole of the paper’s contribution
The room’s leak-test record, with its date	From the room certificate	Whether the room was ever proved dark, and how long ago
The safelight’s label	From the fog test	The safe working time, the distance and the dimmer setting it was measured at
The enlarger certificate	From commissioning	The uniformity map and the flare result, dated, from when everything was known to be right
A print made with the safelight switched off	Work in complete darkness for one print, by feel	Removes the safelight from the differential in one sheet

!Why those two unexposed sheets are the only chemistry this page needs

It is a fair objection that a page about fog cannot avoid the developer, since a developer can produce fog of its own. The two controls answer it, and they do it without needing any print-developer knowledge you have not yet been taught — which matters, because Part XVIII is two parts away and owns that chemistry.

Control 1 was processed in your developer and shows the paper’s density with no exposure at all. Control 2 was processed in the same developer, at the same temperature, for the same time, in the same session, and differs from control 1 in exactly one thing: which packet it came from.

• Both clean — matching the paper’s normal base, and matching each other: the paper and the developer are both excluded, and the fault is in the room, the equipment or the exposure. That is this page’s territory and you may proceed.
• Both grey, equally: the paper is excluded and the developer is not, because the only thing acting on a sheet that was never exposed is the chemistry. That is not this page’s fault — go to Where this page stops.
• Control 1 grey, control 2 clean: the developer is excluded, because it treated both sheets identically. The packet you have been printing from has been fogged, by age, by heat, by damp or by a stray exposure in storage. That is a materials fault, and it is settled by the row in the differential below.

Two sheets, three outcomes, and no chemistry knowledge required beyond “the same bath treated both sheets the same way”. That is what a control is for.

Hints, in increasing order of disruption

Work down this list and stop at the first one that changes the result. Each hint costs more than the one above it, and the top three cost almost nothing.

1. Look at the borders under the easel blades, on a print from tonight and a print from July. Two seconds, and it splits the differential in half.
2. Read the dates on the certificates. ILFORD tell you to change a safelight filter every year and to record the installation date, for exactly this reason. A leak test from eighteen months ago is not evidence about tonight.
3. Sit in the dark for fifteen minutes and look, which is ILFORD’s own instruction before checking a room for leaks, and Kodak’s five-minute white-paper test done properly. Look at the ceiling, the door frame, the vent, the enlarger’s lamphouse while it is on, and every dial, LED and charging light in the room.
4. Print one sheet with the safelight off, working by feel. One sheet, and it settles the largest single question.
5. Cover the paper’s route. Keep the sheet in its packet until the moment of exposure, expose it, and put it straight into the developer, so that its total time out of darkness is seconds. If the fog goes, it is time-dependent — which means the safelight or the room, not the lamphouse.
6. Re-run the room’s leak test, at twice your real handling time, with a control, exactly as the room page sets out. Half an hour of sitting still.
7. Re-run the safelight fog test. Two hours, and it is the definitive answer about the lamp.
8. Re-run the enlarger’s uniformity map at two apertures. Forty-five minutes, and it is the definitive answer about the unevenness.

The diagnosis

Two faults were described in The situation and they are separate problems with separate differentials. Work the fog first, because a fogged sheet makes every unevenness judgement harder.

The fog differential, cheapest evidence first

1. 1Are both control sheets clean?NO, both grey: the developer. Stop here and go to Where this page stops. NO, only the printing packet is grey: paper storage fog; open a fresh packet and check the storage. YES, both clean: proceed.
2. 2Is the border under the blades grey?CLEAN border with a veiled picture area: the fog came down the lens path. Go to the lamphouse and bellows branch. GREY border: the fog reached the paper directly. Continue.
3. 3Does it go away with the safelight off?YES: safelight fog. The lamp, its distance, its setting, its age, or a handling time longer than the safe working time it was measured for. NO: continue.
4. 4Does it have a direction?YES, heavier along one edge: a room leak, and the direction points at it. Sit in the dark and look along that edge. NO: continue.
5. 5Is it a local patch rather than a veil?YES: an indicator, a timer display, a charging light or a phone. Kodak name lighted dials explicitly. Cover it and re-print.
6. 6None of the above, and the fog grows with time out of the packetA room leak with no direction, which usually means the ceiling or a diffuse source such as a frosted door. Re-run the leak test at twice your handling time.

Each branch is decided by evidence you already have or can get for one sheet. Nothing below the third step is reached by most sessions.

The five fog sources, and what tells each one apart

Safelight fog. Grows with the time the paper is out, is even across the sheet, and reaches the borders. Kodak’s language for the mechanism is worth having exactly: a low-level overall exposure given before or after the printing exposure is a super-additive exposure, and virtually all exposures are cumulative — so three four-minute handlings are one twelve-minute exposure as far as the paper is concerned. The cause is usually not that the lamp has changed. It is that the session has: a longer handling time than the one the safe working time was measured for, a lamp that has been moved closer, a dimmer nudged up, or a filter that has aged. ILFORD’s instruction to replace a filter each year and record its installation date is aimed at precisely the component that fails silently.

A room leak. Grows with the time the paper is out and has a direction. That is the discriminator, and it is why the symptom questions ask which edge is worse before anything else. Leaks appear because rooms change: a new security light opposite, a season, a door seal compressed by a summer of heat, a blackout panel put back in the wrong way round.

A lamphouse or bellows leak. The one fog whose border stays clean, because the easel blades masked the paper from anything arriving down the lens path. Kodak name light escaping from an enlarger head among the safelight precautions for exactly this reason. It grows with the exposure time rather than with the handling time, which is a second discriminator: make one print at f/22 for four times as long and it gets worse, not better. The atlas entry carries the full signature.

An indicator or a display. A patch, not a veil, soft-edged, in the same place on every sheet, shaped like whatever was facing the paper. Timer displays, driver indicator LEDs, a charging phone, the standby light on an extractor. Cheap to find — sit in the dark and look at the bench from the paper’s point of view — and cheap to fix, with tape.

Paper age, heat, damp or storage. Indistinguishable from safelight fog by inspection, which is exactly why control 2 exists. ILFORD’s storage instruction is a cool dry place in the original packaging, avoiding high temperature and high humidity, and their keeping claim is up to two years under those conditions. Kodak’s darkroom guide is blunter about the commonest failure: a damp basement without a dehumidifier causes deterioration of films and papers that shows up as weak, mottled pictures, and paper should be stored cool and dry and returned to its original package. The atlas entry has the rest.

📷Why the highlights go first, and why the print looks flat rather than foggy

This is the observation that makes fog hard to recognise, and both manufacturers warn about it in almost the same words. Kodak: poor safelight conditions can produce a loss in photographic quality before actual fogging is visible, and excessive exposure degrades highlights and lowers print contrast before fog shows in the borders. ILFORD: low-level fogging shows as reduced contrast and a lack of clear highlights rather than as visible fog.

The reason is the shape of the paper’s curve. A uniform fog exposure is added everywhere, but what it does depends on where on the curve each tone sits. The highlights live on the long, nearly flat toe, where the tones are separated by hundredths of a density — so a small added exposure both lifts the white point and swallows the separation between the lightest tones at once. The mid-tones sit on the steep part, where the same addition is negligible against what they already received. And maximum black is a ceiling set by the paper — ILFORD publish 2.15 for their current Multigrade RC Deluxe — so it does not move at all until the fog is gross.

So the first symptom of fog is a print that looks slightly flat with unconvincing whites, and the printer’s reflex is to go up a grade. That works, briefly, and it hides the fault while it gets worse.

The unevenness differential

Now the second fault: one corner lighter than the rest. Eight causes, and they sort into three families by two questions — does it change with aperture? and does it follow the paper or the room?

Cause	Where	Signature	The test that names it
Emitter spacing or diffuser distance	Contact printer’s light box	A regular stripe or ripple, or dark corners, fixed relative to the box	The box’s own uniformity map; raise the diffuser and re-map
Mixing-chamber design	Enlarger head	A stripe or bright patch that changes shape with magnification	The head’s T4 at two magnifications
Misalignment	Enlarger	A smooth gradient that is asymmetric — one corner or edge, not all four	The mirror null, in two axes
Lens falloff	Enlarger	All four corners, symmetric, soft-edged, improves on stopping down	Stop down two stops and re-map. Rodenstock draw their measured falloff against the 1 − cos⁴ reference for this reason
Mechanical vignette	Enlarger	One or more corners, hard-edged, unchanged by aperture	Look up through the lens from the corner of the easel: is the whole aperture visible from there?
A condenser out of position	Condenser enlarger	A bright centre with a distinct hot spot, sometimes off-centre	Refit the condenser for the focal length in use; the maker’s manual specifies the spacing
Non-uniform contact pressure	Contact frame	Softness rather than a tone change, worst where the gap is	The frame’s pressure check with a paper strip
Uneven development	The tray	A gradient or a mottle, and it follows the paper	The rotation test below

!The two questions that do most of the work

Does it change with aperture? Optical falloff narrows about the axis when you stop down, so it improves. Metal in the light path is in the way at every aperture. ILFORD’s beginner instruction — turn the ring from full aperture to f/8 to increase edge sharpness and give more even illumination — is the same physics stated as practice.

Is it symmetric about the centre? Lens falloff, a mixing chamber and a condenser are all symmetric about the optical axis by construction. An asymmetric pattern is misalignment or something mechanical, and it is worth checking alignment before anything else because misalignment corrupts every other measurement you would use to diagnose the rest.

The rotation test, which separates the room from the tray

Rotate the paper through 180 degrees and print again

1. 1Notch, cut in the same corner every time — without it you cannot tell which way the sheet went in
2. 2Pattern stays in the room: the equipment — lens, alignment, carrier, light box
3. 3Pattern travels with the paper: the tray — uneven development, or the sheet itself
4. 4The limitation — a centro-symmetric pattern is unchanged by 180 degrees; rotate 90 degrees instead

One extra sheet, and it splits the eight causes above into two groups of four. Do it before you touch the enlarger.

How to run it. Make two prints from the same negative at the same exposure. Between them, rotate the paper through 180° on the easel and nothing else — not the negative, not the carrier, not the easel. Process both in the same way. Then ask where the light area is relative to the room.

• The pattern stayed in the same place on the easel: it is fixed to the equipment. Lens, alignment, carrier, light box.
• The pattern moved with the sheet: it is fixed to the paper. Uneven development, or the sheet itself.

What the course can and cannot say about it. No published account of this test was found in this course’s corpus, so it is offered as reasoning rather than as established practice: rotating the sample while holding the apparatus fixed is the standard way of separating sample-fixed effects from apparatus-fixed ones, and it works here for that reason and no other.

And it has a real limitation, which matters more than the missing citation. A pattern that is symmetric about the centre of the sheet — a bright middle falling to all four corners, which is the commonest shape of all — looks identical after a 180° rotation, so the test says nothing. Where that is your pattern, rotate 90° instead, or accept that this particular test cannot decide it and go to the aperture test.

Working the two faults in the right order

Prove the paper and the chemistry first, with the two controls. Then the room, because room faults affect every sheet including the ones you would use to test the equipment. Then the equipment.

Change one thing at a time and re-print after each. This is the rule that people abandon at about the forty-minute mark, and abandoning it is why the same evening gets spent twice: change the developer and the safelight distance and the aperture together, get a good print, and you have learnt nothing except that some combination works.

The fix

The fix follows the diagnosis and most of them are cheap.

Diagnosis	The fix	The test that confirms it
Safelight fog from a longer session	Shorten the handling: paper in the packet until exposure, emulsion down on the bench, the dish out of the direct pool	One print with the shortened handling, against tonight’s
Safelight fog from a moved lamp or a raised dimmer	Put it back to the distance and setting on its label. Permitted time goes as the square of distance	The label, then a repeat print
Safelight fog from an aged filter or emitter	Replace it, and record the installation date as ILFORD instruct	A full fog test, which is the only real answer
A room leak with a direction	Find it by sitting in the dark; black tape for small, heavy cloth for large, which is Kodak’s own advice	Re-run the leak test at twice your handling time, with a control
A lamphouse or bellows leak	Tape or felt at the seam from the inside; a patch on the bellows	The capped-lens test from commissioning
An indicator or display	Tape, a hood, or move it behind the enlarger column	One print with it covered
Paper storage fog	A fresh packet, and a cool dry storage place in the original packaging	Control 2 becomes control 1 for the new packet
Lens falloff at full aperture	Print two stops down, and burn the corners by the amount the map says	The uniformity map at the new aperture
A mechanical vignette	Remove the obstruction: file the carrier, push the filter drawer home, remove a hood	Re-map; a hard-edged corner that has gone is proof
Misalignment	Shim and lock, then re-check after moving the head	The mirror null in two axes
Light-box unevenness	Raise the diffuser, add a second, or extend the emitter overhang	The box’s own uniformity map
Uneven development	A larger dish, continuous agitation, and the same agitation for every sheet	The rotation test again
Non-uniform contact pressure	Re-tension the springs, replace set foam, check the baseboard for cupping	The paper-strip pressure check

And one fix that is not a fix. Going up a grade because the print looks flat treats fog as a contrast problem. It works for one evening, it hides the cause, and the cause gets worse. If you have gone up a grade this session, go back down before you start diagnosing, or you are measuring two things at once.

What to record

In the notebook, tonight, and then into the calibration library so the same evening is not spent twice.

Record	Why
The date, and what had changed since the last good session	The answer is nearly always in this line: a season, a lamp, a packet, a moved bench
The two control sheets, kept, labelled and dated	They are the floor every later comparison is read against
Which of the four symptom questions gave which answer	So the reasoning can be checked, not just the conclusion
The fault, the test that proved it, and the tests that excluded the others	An exclusion is a result and it is worth as much as the finding
What was changed, and only what was changed	One thing at a time, written down as one thing
The re-test result after the fix	A fix that was not re-tested is a hypothesis
Updated entries on the room certificate, the safelight label or the enlarger certificate	The certificates are the memory. A fault found and not written down is a fault found once
Anything you could not decide, and why	The most valuable line in the book next time

Where this page stops

Stated here because it is a boundary rather than an afterthought. This page owns fog sources and illumination uniformity — the room and the equipment. It does not own the print chemistry, and there are three results that send you out of it.

• The unexposed sheet from a fresh, unopened packet also comes out grey. Nothing in the room touched that sheet. The only thing that acted on it is the developer.
• The blacks are dull and there is no fog anywhere — clean borders, clean whites, and a maximum black that is not black. That is a failure to reach the paper’s ceiling, and the ceiling is chemistry.
• The whites are stained rather than veiled — yellowish or brownish rather than a neutral grey. A stain is a residue, not an exposure.

All three belong to Part XVIII’s break/fix page, “The Print That Will Not Go Black”, which comes after the print chemistry that explains them: developer age, dilution, temperature and contamination, fixer carry-over and clearing, paper grade and exposure technique. That part is not yet written, so this page names it rather than links to it. Part XXVIII’s print faults and poor maximum black keeps the troubleshooting atlas entry for the same family.

How to tell which page you are in, in one sentence. If your whites are the problem, you are here. If your blacks are the problem and the whites are clean, you are not.

Questions

1. A print has a grey veil across the picture area and a clean white border under the easel blades. Name the two candidate causes this observation leaves, and the one test that separates them.
2. Both control sheets come out at the same faint grey. Which two members of the differential does that exclude, which does it implicate, and what does this page do next?
3. A printer reports that their blacks improved after painting the wall behind the enlarger matt black. Name what else is likely to have changed at the same time, and design the test that would settle the claim.
4. Explain why a fogged print looks flat rather than foggy, arguing from the shape of the paper’s characteristic curve rather than from experience.
5. Your unevenness is a smooth fall from a bright centre to all four corners. You run the rotation test and the pattern is unchanged. What has the test told you, and what has it not?
6. Design the minimum sequence of tests that distinguishes safelight fog from a room leak in one evening, and say what each result rules out.
7. A print made with the safelight off is still fogged, the border is grey, and the fog does not have a direction. What is left in the differential, and what is the cheapest next test?
8. You have spent an evening and found nothing, but you notice the session log says you now print for two hours where you used to print for forty minutes. Explain, using Kodak’s own term, why nothing being broken is consistent with the prints having got worse.

Further work

Build your own signature sheet. Deliberately produce each of the six faults on a sheet of paper — fog one with the safelight at half the distance, one with the lamphouse taped open, one with a torch pointed at the ceiling, one with a timer display uncovered — and file the six prints together, dated, with what you did on the back. Half an hour of deliberate sabotage is worth more than any drawing, this page’s included.

Measure your handling time, honestly. Watch in hand, during a real session: from opening the packet to the sheet entering the fixer. Compare it with the number your safe working time was measured for. Most printers find their real handling time has grown by half since the session in which they measured it, which is the commonest cause of fog appearing in a room where nothing has changed.

Settle the rotation test’s limitation. Run it at 90° as well as 180° on a deliberately symmetric fault and on a deliberately asymmetric one, and record what each rotation could and could not decide. The course could not source this test at all; a careful record of what it actually distinguishes is a real contribution.

Put a number on your room’s contribution. Print two identical maximum-black patches, one in the room as it is and one with black cloth over every pale surface within a metre of the enlarger. If they differ, your walls are costing you black, and you have measured it — which is the question commissioning’s F3 asks and which this course has no result for.

Recap

The session began with two faults and no evidence, and the first move was not to change anything. Two unexposed sheets — one from the packet in use and one from a fresh packet — are the whole of the chemistry this page needs: they exclude the paper and the developer between them, using no knowledge beyond “the same bath treated both sheets the same way”, and their three possible outcomes decide whether you are on this page at all.

The fog differential then runs on patterns rather than magnitudes. A clean border under the easel blades with a veiled picture area means the light came down the lens path — the lamphouse or the bellows. A grey border means it reached the paper directly, and after that the questions are whether it goes away with the safelight off, whether it has a direction, and whether it is a patch rather than a veil. Paper storage fog is indistinguishable from safelight fog by inspection, which is precisely why control 2 exists.

Fog shows in the highlights first because they sit on the long flat toe of the paper’s curve, so the first symptom is a print that looks slightly flat with unconvincing whites — and the reflex of going up a grade hides the fault while it grows. Both manufacturers warn about it in nearly the same words.

The unevenness differential sorts eight causes with two questions: does it change with aperture, and is it symmetric? Optics improve on stopping down and metal does not; falloff and a mixing chamber are symmetric by construction and misalignment is not. The rotation test adds a third cut — the room or the tray — and it has a real limitation, which is that a centro-symmetric pattern survives a 180° turn unchanged.

Then the discipline: paper and chemistry, then the room, then the equipment; one change at a time; re-test after each; and everything into the record, including the exclusions. And the boundary, stated plainly: whites are this page, blacks are Part XVIII.

Check your understanding

Question 1. A print shows an even grey veil across the picture area and a perfectly clean white border where the easel blades masked the paper. What does that single observation establish?

• That the safelight is fogging the paper
• That the fog arrived through the lens path - the lamphouse, the bellows or flare - because the blades masked the border from that and from nothing else
• That the paper is out of date
• That the developer is exhausted

Show the answer and why

Answer: That the fog arrived through the lens path - the lamphouse, the bellows or flare - because the blades masked the border from that and from nothing else

The easel blades are a mask against light travelling from the lens to the paper, and against nothing else. A safelight, a room leak, an indicator or a fogged packet all reach the whole sheet including the strip under the blades, so any of those would grey the border too. That single look therefore splits the differential in half before any sheet is spent, which is why it is the first of the four symptom questions. Note also the second discriminator that follows from it: a lens-path fog grows with the exposure time rather than with the handling time.

Question 2. You process an unexposed sheet from the packet you have been printing from and an unexposed sheet from a fresh unopened packet, in the same bath in the same session. Both come out at the same faint grey. What follows?

• The room is leaking, and the leak test must be re-run
• The paper is excluded, because two different packets behaved identically; the developer is implicated, because it is the only thing that acted on a sheet that was never exposed - so the fault is not this page and goes to Part XVIII
• The safelight is fogging both sheets
• Nothing can be concluded without a densitometer

Show the answer and why

Answer: The paper is excluded, because two different packets behaved identically; the developer is implicated, because it is the only thing that acted on a sheet that was never exposed - so the fault is not this page and goes to Part XVIII

Neither sheet was ever exposed to anything, so nothing in the room can have reached them - which excludes the safelight, the room and the lamphouse in one step. Two packets from different batches behaving identically excludes the material. That leaves the chemistry, and the whole point of the two-control design is that it reaches that conclusion without the reader needing to know any print-developer chemistry: the argument is entirely about what acted on what. This is the boundary the page states in Where this page stops, and crossing it is the correct outcome rather than a failure of the page.

Question 3. Every print is lighter towards all four corners, symmetrically. Stopping down two stops halves the effect. What is the diagnosis?

• A mechanical vignette in the carrier
• Lens illumination falloff, which narrows about the axis when you stop down - which is exactly why ILFORD tell a beginner to go from full aperture to f/8 for more even illumination
• Misalignment of the negative stage
• Uneven development in the tray

Show the answer and why

Answer: Lens illumination falloff, which narrows about the axis when you stop down - which is exactly why ILFORD tell a beginner to go from full aperture to f/8 for more even illumination

Two features settle it. Symmetry about the axis rules out misalignment, which by its nature makes the geometry different on two sides. Improvement on stopping down rules out anything mechanical, because a piece of metal in the path is in the path at every aperture. What is left is the lens own falloff, whose geometric reference is the fourth power of the cosine of the field angle - the curve Rodenstock draw on every one of their published performance charts so that a measured curve can be judged against it. Uneven development is excluded separately by the rotation test, since a development pattern travels with the sheet.

Question 4. Why does this page insist on running the rotation test before touching the enlarger, when it cannot decide a symmetric pattern?

• Because it is the most accurate test available
• Because it costs one sheet and splits eight causes into two groups of four - equipment-fixed against paper-fixed - and it is worth doing before any test that involves changing the equipment and destroying the state you are diagnosing
• Because development faults are the commonest cause of unevenness
• Because the enlarger must be warmed up first

Show the answer and why

Answer: Because it costs one sheet and splits eight causes into two groups of four - equipment-fixed against paper-fixed - and it is worth doing before any test that involves changing the equipment and destroying the state you are diagnosing

It is a question of order and of cost rather than of precision. Every equipment test - stopping down, re-mapping, shimming, refitting a condenser - changes the machine, and once changed you cannot go back to the state that produced the fault. The rotation test changes nothing, costs one sheet, and removes half the differential when it works. Its limitation is real and is stated: a pattern symmetric about the centre of the sheet looks the same after a 180 degree turn, so on that pattern the test is silent and you go to the aperture test instead.

Question 5. A printer finds fog in a room where nothing has been moved, no bulb changed and no new packet opened. Their session log shows they now print for two hours where they used to print for forty minutes. Using Kodak term, explain the result.

• The safelight filter has aged and must be replaced
• Exposures are cumulative and a low-level overall exposure before or after the printing exposure is super-additive, so tripling the handling time triples the safelight dose - the lamp has not changed but the session has, and the safe working time it was measured for has been exceeded
• The paper has deteriorated over two hours in the room
• The developer has oxidised over the longer session

Show the answer and why

Answer: Exposures are cumulative and a low-level overall exposure before or after the printing exposure is super-additive, so tripling the handling time triples the safelight dose - the lamp has not changed but the session has, and the safe working time it was measured for has been exceeded

A safe working time is a duration, not a property of a lamp, and it was measured for a stated handling time at a stated distance and setting. Kodak state that virtually all exposures are cumulative and give the name super-additive exposure to the low-level overall exposure a safelight adds before or after the printing exposure, so three forty-minute sessions worth of handling in one evening is one long safelight exposure as far as the paper is concerned. Filter ageing is a genuine and separate cause, which is why ILFORD tell you to change a filter yearly and record the date; but nothing here points to it, and the log points straight at the handling time.

Question 6. Which of these belongs to this page, and which is handed on?

• Grey whites belong to Part XVIII; dull blacks belong here
• Grey whites belong here, because fog and stray light lift the toe of the paper curve; dull blacks with clean whites belong to Part XVIII, because failing to reach the paper ceiling is a chemistry result
• Both belong here, since both are print faults
• Both belong to Part XVIII, since both involve the developer

Show the answer and why

Answer: Grey whites belong here, because fog and stray light lift the toe of the paper curve; dull blacks with clean whites belong to Part XVIII, because failing to reach the paper ceiling is a chemistry result

The split follows the mechanism. Fog and flare add exposure everywhere, and on the paper curve that does most where least was received - the toe, which is the highlights - so a veiled white is the signature of light arriving where it should not. Maximum black is a ceiling set by the paper and reached by development; a black that is not black means the sheet did not get there, which is exposure or chemistry rather than stray light. The page states the one-sentence version deliberately: whites here, blacks there. And a stain rather than a veil is a third case and a residue, which belongs with the fixing and washing chemistry.

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