The Emulsion Under Stress: Reticulation, Scratches, Pinholes and Drying Marks

Nine of the defects in this course’s atlas have nothing to do with silver. They are things that happened to the gelatin, and they follow from four properties of that material:

1. It swells in water rather than dissolving, so a processed emulsion in a bath is a wet sponge several times its dry thickness.
2. While it is swollen it is soft, and anything that touches it leaves a record.
3. It shrinks as it dries, and whatever was dissolved in the water stays behind.
4. When dry it is an insulator, so it accumulates charge and eventually discharges.

Learn those four and the nine defects stop being a list to memorise.

The layer, through the process

A film through the process, as a layer that changes thickness

Drawn for readability, not to scale: the base is over a hundred times the emulsion's thickness, and drawing that honestly would make the emulsion invisible. The base thicknesses given are ILFORD's published figures for HP5 Plus. No source in this course's corpus publishes a swelling ratio for a processed emulsion, so the swollen state is described in words above rather than drawn as a multiple. Layer depths are drawn to be readable, not to scale: on real film the base is roughly a hundred times the emulsion, and drawn honestly the emulsion would vanish. Any thickness given in the labels is the real one.

Hardening, and what it buys

A hardener cross-links the gelatin network, so the layer swells less, melts at a higher temperature or not at all, and resists abrasion better. Kodak’s 1928 primer treats alum hardening as routine and prescribes it against exactly the failures on this page.

Modern films are hardened at manufacture, and that changes the whole tone of the classic advice. ILFORD’s HYPAM sheet states it plainly: a fix hardener “is no longer generally recommended because modern camera films are sufficiently hardened at manufacture”. The MULTIGRADE sheets go further and recommend against a hardening fixer, because it reduces washing efficiency. Part XI works through the trade — hardening against wash time and toning receptivity — and reaches the same place.

What follows for this page is that most of the classic warnings about temperature discipline were written for materials that were far more vulnerable than yours. They have not become wrong; they have become less urgent for a bought film, and they remain fully urgent for a hand-coated emulsion, which is the case the hardening fixer was invented for and which has not gone away.

Reticulation

What you see. A coarse wrinkling over the whole layer, visible in reflected light and, in bad cases, as a texture that prints. It has no direction and no relationship to the picture, because it is a property of the gelatin rather than of the image in it. It covers the rebate as thoroughly as the frame.

The mechanism, which is certain. Kodak’s 1928 primer states it in a sentence: all solutions must be kept at the same temperature “in order to avoid sudden contractions or expansions of the gelatin which may result in detaching the film from its support or in the production of reticulation, i.e., a coarse wrinkling all over the film”. A swollen network moved abruptly into a bath that swells it much less has to contract, and a network that contracts faster at its surface than through its thickness buckles.

How large a shock it takes on a modern film is genuinely disputed, and the course does not settle it. The atlas entry carries the dispute in full: the 1928 primer describes it as a real risk under extreme temperatures with the materials of its day, while modern practitioners frequently report being unable to produce it deliberately on current hardened films. The course has found no modern manufacturer statement establishing either position and does not pick one.

Both sides agree on the control, which is the part you can act on: keep the baths close. ILFORD’s published tolerance for film is that all process solutions be at the same temperature or at least within 5 °C of the developer.

✕Clumped grain is not reticulation, and the two are confused constantly

A negative developed hot, or in an energetic developer, or pushed hard, can show a coarse, mealy texture that people call reticulation. Usually it is not.

Reticulation is a wrinkling of the gelatin surface. It is a physical deformation of the layer, it is visible in reflected light on the film itself as a texture you can see by tilting it against a lamp, and it covers the rebate.

Clumped grain is an image structure. It is visible only through the image, only under magnification, only where there is silver — and it is absent from the rebate, because there is no image there.

So the discriminator costs nothing: tilt the film against a light and look at the rebate. A texture in the rebate is the gelatin. No texture in the rebate, and a coarse appearance in the picture, is grain.

Frilling and blisters

Frilling is the emulsion lifting away from its support at the edges of a sheet or a strip — the substratum bond failing where the layer’s edge is exposed and where it swells most freely. Abney’s 1885 treatise already discusses the substratum’s role in preventing frilling and blistering, and records that plates frill with some developers and not others, which tells you the fault is a bond stressed by swelling rather than a defect of manufacture.

The over-swelling route is set out by the 1928 primer, and it is a warning about developers rather than about temperature: alkalis soften the gelatin of the emulsion, and “too alkaline a developer will produce over-swelling and will give trouble with frilling or blisters in warm weather”. Alkali plus warmth is the combination.

Blisters have a second and much more specific cause, and the evidence for it is unusually good.

⚗Carbonate meets acid, and the gas has nowhere to go

The 1928 primer states the mechanism directly: “When the sodium carbonate of the developer is neutralized by the acid in the fixing bath, carbon dioxide gas is evolved which produces blisters if the gelatin is too soft to withstand the disruptive action of the gas.”

The conditions it names are a fixing bath with an excess of acid together with films that are not rinsed sufficiently, or a strongly acid rinse bath; and it adds that the trouble is more likely in hot weather and especially when the bath is not hardening sufficiently.

Its description of the dry appearance is the part worth memorising: on dry film, blisters appear as tiny crater-like depressions when examined by reflected light.

The corroboration is a product. Kodak Limited’s 1944 formulary introduces Kodalk, an alkali intermediate in activity between sodium carbonate and borax, and sells it on exactly this: films developed in a Kodalk developer “will not blister when placed in an acid fixing bath, even at high temperatures”, because Kodalk “does not evolve carbon dioxide on acidifying” — with the added benefit of less tendency to precipitate aluminium sulphite sludge from alum fixing baths.

A manufacturer marketing a carbonate-free alkali because it removes the blistering risk is about as strong a confirmation of a mechanism as historical literature offers. Two independent Kodak publications, sixteen years apart, and one of them staking a product on it.

!Where the sources say the gas is evolved, and where they do not

The mechanism above is well supported. One detail of the way it is usually retold is not, and the course reports the difference rather than smoothing it.

The account you commonly meet places the gas evolution at a strongly acid stop bath. Both Kodak sources place it at the acid fixing bath, and the 1928 primer names “a strongly acid rinse bath” as an additional condition rather than as the principal one.

The chemistry does not care which acid bath it is: carbonate plus acid gives carbon dioxide wherever they meet. But the conditions the sources give — an over-acid fixer, and insufficient rinsing before it — point at the fixer, and the prevention follows from that: a rinse or a stop bath between developer and fixer, and a fixer whose acid content is right.

RC blisters are a further step and the course cannot take it from its corpus. ILFORD’s MULTIGRADE RC sheet gives a hot-air drying limit of 85 °C, and warns that RC papers must not be glazed, ferrotyped or dried on a drum or flatbed glazer because the polyethylene can stick to the glazing surface. It does not name blisters, and no source in the corpus attributes a blister on an RC print to drying heat. What the corpus supports is the gas mechanism above, which applies to an RC print exactly as it applies to a film: a carbonate paper developer carried into an acid bath, in a layer sandwiched between two impermeable polyethylene skins that give the gas nowhere to escape sideways. That last clause is the course’s inference and is marked as one. Treat the drying limit as a published limit worth respecting, and the blister attribution as unestablished.

Physical damage while the layer is wet

A swollen emulsion is soft, and everything that touches it leaves something.

Fingerprints. A print of the ridges, made in the layer itself rather than in grease on top of it, and permanent. On a wet emulsion the mark is physical; on a dry sheet of unexposed paper a fingerprint is chemical, because whatever was on the finger — fixer especially — reacts with the emulsion, and that fault belongs to the chemistry in the bottle.

Tong marks. Two small crescents or a pair of parallel indentations, at the edge or wherever the tongs gripped, appearing as a density change as well as a mark because pressure on a wet emulsion affects development locally as well as deforming the layer.

Squeegee marks. A pair of parallel lines running the length of the film or the print, where the blade dragged. ILFORD’s own instruction is to use a clean squeegee or chamois to wipe film before hanging it, in order to avoid drying marks — so the squeegee is prescribed, not forbidden. The word doing the work is clean: ILFORD’s first-film guide warns to take care because any grit caught in the squeegee “will scratch the whole film”, which is one of the few faults that turns a whole roll into a loss in one second.

The rule that follows from all three. Touch a wet emulsion as little as possible, and where you must, touch only what will be trimmed. The Library of Congress’s handling guidance states the archival version for finished material: freshly washed hands, clean lint-free cotton or inert plastic gloves such as nitrile, and no contact with the image surface at all; when a photograph must be moved or turned, support it on a piece of rigid board rather than flexing it.

Scratches, and the question that identifies them

The diagnostic question is: which side of the base is it on? Everything else about a scratch — length, direction, whether it prints — is secondary.

Which side is the scratch on, and how the light tells you

1. 1Emulsion-side scratch — Silver has been physically removed. Reads light on the negative and prints dark. Irreversible.
2. 2Base-side scratch — A groove in clear plastic. Scatters light rather than absorbing it, so it reads dark on a light box and prints light.
3. 3The refractive-index test — A base-side scratch can be made to vanish by wetting the base; an emulsion-side one cannot. This is the confirming test.
4. 4The loupe test — Focus a loupe on the emulsion surface, then on the base surface. The scratch is sharp on one and not the other.

Two grooves of the same size in the same piece of film, on opposite faces, behaving oppositely. It is the single most useful discrimination in this part, because it says where in the chain the mark was made.

An emulsion-side scratch was made after the emulsion was soft — which means in the tank, in the wash, on the squeegee, on the hanging line, or in handling afterwards. Silver has been removed, so the scratch prints as a black line and nothing will put it back.

A base-side scratch is usually mechanical and usually earlier: the cassette’s felt light trap, the camera’s pressure plate, the film path, or grit. Kodak’s Z-133 lists the laboratory versions — dirt or chemical build-up on rollers, squeegees or racks; stuck, misaligned or dirty rollers; and “dirt in camera”, whose recommended corrective action in a commercial laboratory is, revealingly, “notify customer”. No silver has been removed, so the mark is a lens rather than an absorber, and it can often be reduced by filling the groove — the trade’s traditional answers are a wet-mounting fluid or a diffusion enlarger’s scattered illumination, both of which work by refusing to give the groove a directional beam to bend.

A scratch that repeats down the whole length of a film, in the same place, is a piece of equipment. That is the most useful thing the shape tells you. A continuous line at a constant distance from the edge was made by something the film ran past.

Cinch and pressure marks

What you see. Crescents or half-moons, a few millimetres across, usually in groups, and of increased density.

Why increased. This is what separates them from every mark on this page so far. Pressure on an emulsion before development makes the pressed region more developable — the mechanical work creates developable centres — so the mark is a density change rather than a removal. Kodak’s Z-133 catalogues them under Pressure marks — plus-density areas (e.g. half-moons, crescents, etc.), with three causes: poor film handling, excessive tension, and camera malfunction.

Where they come from at home. Pulling a loose film tight in its cassette by turning the spool — which is where “cinch” comes from — and forcing a film onto a spiral reel that is damp or misaligned. Both apply sharp local bending to a strip that is held at its edges.

How they differ from a scratch. A scratch is a groove and a cinch mark is not: run a fingernail across it and you feel nothing. A scratch is generally a straight line and a cinch mark is a crescent. And the density goes the other way — a scratch on the emulsion side is a loss, a cinch mark is a gain.

Pinholes, and why one name for three faults is misleading

Small clear spots in the developed image get called pinholes whatever produced them, and the three producers have nothing in common but the appearance.

Three pinholes, three causes, three preventions

1. 1Gas evolved in the layerA carbonate developer meeting an acid bath: carbon dioxide, evolved inside a soft layer, disrupting it. The 1928 primer calls the result a blister and describes it on dry film as tiny crater-like depressions in reflected light. Prevention: rinse or stop between developer and fixer, correct fixer acidity, and a carbonate-free alkali if the problem persists.
2. 2A bubble or a dust particle in a hand-coated layerA coating fault, made before the plate was ever exposed. The hole goes right through the emulsion to the support, so it is perfectly clear and its edges are the shape of the bubble. Prevention belongs to Part V's coating pages, and the atlas entry for coating bubbles and pinholes is owned there.
3. 3A dust particle on the plate before exposureThe particle masked the light, so no latent image formed under it and the fixer removed the halide. The hole is the shape of the particle, and on a plate exposed in a holder it is often accompanied by others in the same area. Prevention is cleanliness of the holder and the darkslide, not chemistry.

The three are distinguished by their edges and their company: a gas crater has a raised rim and looks like a depression in reflected light, a coating bubble is a clean round hole through the layer, and a dust shadow has an irregular outline and usually has friends nearby.

Drying marks and water spots

What you see. Marks with a distinct edge, often circular or tear-shaped, sometimes with a paler centre and a darker rim, usually towards the lower part of a hanging film or wherever a drop sat.

What they are, and it is the point of the section. They are not dirt on top of the gelatin. As the last of the water evaporates, everything dissolved in that water is left in a shrinking volume, and by the end it is concentrated in the layer itself. What you have is a local change in the gelatin — its density, its refractive index, and sometimes a deposit of salts within it — which is why so many of them will not simply wipe off.

Why hard water makes them worse is immediate from that account: hard water carries more dissolved solid to leave behind. Kodak’s own processing sheets give the remedy in one line — “to reduce drying scum, mix KODAK PHOTO-FLO Solution with distilled water in areas that have hard water” — and Kodak Limited’s 1944 formulary had already published the same practice, with a refinement worth having: “for hard water use a smaller amount of wetting agent”, and where the water is very hard and tends to deposit a scum, “give the final rinse in distilled water containing this addition of wetting agent”.

Why a wetting agent works. It lowers the surface tension of the rinse water so that the film drains as a continuous sheet rather than breaking into drops. No drops, no local concentration, no marks. ILFORD publish ILFOTOL’s starting dilution as 5 mL per litre (1+200) and add two cautions that matter more than the number: the dilution needed depends on your water, your equipment and your drying method; and “either too little or too much wetting agent can lead to uneven drying”. Too much is a real fault rather than a surplus without consequence, and excessive agitation of the solution makes it foam.

Which ones can be removed and which cannot. Kodak’s Z-133 treats water marks as a preventable process fault and gives five causes with five corrective actions — water collecting in the perforations, meaning the wetting agent is wrongly diluted; water running down from the clips; water splashed on the film; inadequate drying, meaning the drying temperature is too low; and film drying too quickly, meaning it is too high. All five are prevention. None is a treatment.

For the treatment question the course’s honest position is narrower than the folklore. A deposit sitting on the surface can sometimes be removed by rewashing and re-rinsing with a correctly diluted wetting agent, and drying properly the second time — the material is water-soluble salt and the layer will swell again to release it. A mark that is a change in the gelatin will not come back, because nothing has been added that can be taken away. Neither the manufacturer sheets nor the conservation guidance in this course’s corpus states which case a given mark is, so the practical rule is: try rewashing once, on the understanding that it may do nothing, and do not escalate to solvents or abrasives on an original.

The temperature window for drying is published: ILFORD ask for 30–40 °C in a drying cabinet, or room temperature in a clean dust-free area. Faster is not better — Kodak names film drying too quickly as a cause of water marks and gives “reduce the drying temperature” as the fix.

Static discharge marks

What you see. Kodak’s Z-133 description is precise enough to use as an identification: “branch-like marks, circular spots with dark centers, row of spots (often surrounded by fogged areas)”. They are dark on the negative, because they are exposure — light emitted by an electrical discharge, inside the cassette or the camera, recorded by the film like any other light.

When it happens. Film is an insulator moving over other insulators. Winding or rewinding quickly, especially in dry air, separates charge; when the potential is high enough it discharges, and the spark emits light. Kodak’s corrective actions name all three variables: maintain moderate levels of humidity and temperature in the areas where film is handled, handle film carefully, and separate rolls and sheets slowly and carefully.

Why the shapes. A branching mark is a discharge propagating across a surface — the same tree structure a lightning flash has, for the same reason. A row of spots is discharge at intervals as the film moved past a fixed point. A dark centre with a lighter surround is a point discharge photographed from very close.

How to be sure it is static and not a light leak. Three tests. Static marks are sharp and branching or punctate; a leak is a gradient. Static marks appear anywhere on the film including across frame lines and in the rebate, without respecting the geometry of the camera back. And static is seasonal and situational: it appears in winter, in heated rooms, on fast rewinds, and disappears when the air is damp.

One prevention worth noting is that ILFORD list an anti-static treatment among the uses of their wetting agent — which is about processed film in storage rather than about film in the camera, but is worth knowing when the marks appear during handling of dry negatives rather than during shooting.

What can be treated and what cannot

An honest list, because the folklore is generous and the chemistry is not.

Sometimes treatable. A surface deposit — a water spot that has not entered the layer, a salt scum — by rewashing and correct re-rinsing. A base-side scratch, by refractive-index matching at the printing stage rather than by repairing the film. Dust on the base, by careful cleaning with clean hands, a clean cloth and nothing abrasive.

Not treatable. Reticulation: the layer has set in its new shape. Frilling: the bond is broken. An emulsion-side scratch: silver has been removed. A pinhole of any of the three kinds: there is nothing there. A cinch mark: the development that responded to the pressure has already happened. A static mark: it is a developed image of a spark.

Retouching, and its honest limits. Spotting a print — filling a white spot with dye — has been standard practice for a century and works well on small marks. It does not work on a texture, on a mark that occupies a large area, or on anything in a continuous tone that has to match its surroundings over a distance. And the Library of Congress’s guidance is explicit that marking originals with ink or felt-tip pens, and repairing them with pressure-sensitive tape, are examples of negligence rather than of conservation: retouch the print, never the negative you might want again.

Atlas entries this page owns

Nine entries in the troubleshooting atlas belong here: reticulation, frilling, blisters, emulsion-side scratches, base-side scratches, cinch and pressure marks, pinholes, drying marks and water spots, together with static discharge marks.

Two boundaries are worth stating. Coating defects in a hand-made emulsion stay with Part V — coating bubbles and pinholes and coating mottle and drying marks are that part’s, because they belong to a material the student made rather than bought. And RC blisters are claimed by the print page, because their context is paper handling and drying.

Recap

Four properties of gelatin generate the whole family: it swells, it is soft while swollen, it shrinks as it dries, and it holds charge when dry. Modern films are hardened at manufacture, which makes the classic temperature warnings less urgent for a bought film and no less urgent for a hand-coated one. Reticulation is a wrinkling of the layer that covers the rebate, and it is told from clumped grain by looking at the rebate. Blisters come from carbon dioxide evolved when a carbonate developer meets an acid bath — a mechanism Kodak stated in 1928 and confirmed in 1944 by selling an alkali that avoids it. A scratch is identified by which side of the base it is on, because the emulsion side has lost silver and the base side has only lost its flatness. Crescents are plus-density pressure marks and are not scratches. Three different faults are called pinholes. Drying marks are a change in the gelatin rather than dirt on it, which is why prevention — a wetting agent correctly diluted, distilled water where the supply is hard, and a drying temperature between 30 and 40 °C — is worth more than any treatment.

Check your understanding

Question 1. A negative shows fine parallel marks running its whole length. What tests determine which side they are on, and what does each answer implicate?

• Print it and see whether the lines are black or white; black means the base
• Focus a loupe on each surface in turn, and wet the base with a little clean water on a swab. A mark that is sharp when the loupe is focused on the emulsion, and unchanged by wetting the base, is an emulsion-side scratch — made after the layer was soft, so in the tank, the wash, the squeegee or later handling. A mark that is sharp on the base surface and fades when the base is wetted is a base-side scratch — usually the cassette felt, the pressure plate or the film path.
• Measure the density of the line with a densitometer
• Compare the marks with the sprocket pitch

Show the answer and why

Answer: Focus a loupe on each surface in turn, and wet the base with a little clean water on a swab. A mark that is sharp when the loupe is focused on the emulsion, and unchanged by wetting the base, is an emulsion-side scratch — made after the layer was soft, so in the tank, the wash, the squeegee or later handling. A mark that is sharp on the base surface and fades when the base is wetted is a base-side scratch — usually the cassette felt, the pressure plate or the film path.

The wetting test works because a base-side scratch is a groove in clear plastic that bends light out of the viewing direction rather than absorbing it; filling the groove with a liquid of similar refractive index removes the bending and the mark all but disappears. An emulsion-side scratch has physically removed silver, and nothing you put in the groove can put it back. The consequence for the diagnosis is that the two implicate different halves of the chain: one is wet-side handling, the other is the camera and the cassette.

Question 2. Name three different causes of a pinhole and say what distinguishes their appearance.

• Dust, dust and dust, in three different places
• Gas evolved inside the layer where a carbonate developer met an acid bath, which reads as a crater-like depression with a rim in reflected light; a bubble or dust particle trapped in a hand-coated emulsion, which is a clean round hole right through the layer to the support; and a dust particle lying on the plate before exposure, which masked the light so that no latent image formed, leaving an irregular hole shaped like the particle and usually with others nearby
• Over-fixing, under-fixing and over-washing
• Air bells, surge marks and static marks

Show the answer and why

Answer: Gas evolved inside the layer where a carbonate developer met an acid bath, which reads as a crater-like depression with a rim in reflected light; a bubble or dust particle trapped in a hand-coated emulsion, which is a clean round hole right through the layer to the support; and a dust particle lying on the plate before exposure, which masked the light so that no latent image formed, leaving an irregular hole shaped like the particle and usually with others nearby

The single name is the problem: three unrelated events produce a small clear spot, and each has its own prevention — a rinse and correct fixer acidity for the first, coating technique for the second, and cleanliness of the holder for the third. The edge is the discriminator. A gas crater is a deformation of the layer and shows as a depression in reflected light; a coating bubble is a clean absence with the shape of a bubble; a dust shadow has the ragged outline of the particle that made it.

Question 3. A film is transferred from a developer at 20 °C into a wash at 30 °C. What happens to the gelatin, and what would have to be true of the film for it to survive?

• Nothing at all; ten degrees is within normal tolerance
• The layer swells further and more rapidly, because warmth increases swelling and plain water swells it more than a salt solution does; whether it survives depends on how well it is hardened — a modern film hardened at manufacture will very probably be unaffected, while a lightly hardened hand-coated layer is at real risk of reticulation or frilling. ILFORD's published tolerance is all solutions within 5 °C of the developer, so this transfer is twice that.
• The layer contracts, because water is less dense than developer
• The image dissolves, because gelatin dissolves in warm water

Show the answer and why

Answer: The layer swells further and more rapidly, because warmth increases swelling and plain water swells it more than a salt solution does; whether it survives depends on how well it is hardened — a modern film hardened at manufacture will very probably be unaffected, while a lightly hardened hand-coated layer is at real risk of reticulation or frilling. ILFORD's published tolerance is all solutions within 5 °C of the developer, so this transfer is twice that.

Two things drive the swelling in the same direction here — the temperature rise and the move from a salt solution into plain water — so it is a larger stress than the temperature alone suggests. Note what the honest answer contains: a mechanism that is certain, a published tolerance that the transfer breaks, and a genuine uncertainty about the outcome on a modern hardened film, which the course reports rather than resolving. Gelatin does not dissolve in warm water at these temperatures; it swells, and a fully melted layer is a different and much hotter failure.

Question 4. Why does the course describe the blister mechanism as well established but the attribution of RC blisters to drying heat as unestablished?

• Because RC paper is too modern for the historical sources
• Because two independent Kodak publications support the gas mechanism — the 1928 primer states that carbon dioxide from the developer's carbonate meeting the fixing bath's acid produces blisters, and the 1944 formulary markets Kodalk on the grounds that it does not evolve carbon dioxide on acidifying and so eliminates the risk — while no source in the corpus attributes a blister on an RC print to drying temperature; the datasheet gives an 85 °C hot-air limit and a warning about glazing, and names no blister
• Because blisters cannot occur on resin-coated paper
• Because heat has no effect on polyethylene

Show the answer and why

Answer: Because two independent Kodak publications support the gas mechanism — the 1928 primer states that carbon dioxide from the developer's carbonate meeting the fixing bath's acid produces blisters, and the 1944 formulary markets Kodalk on the grounds that it does not evolve carbon dioxide on acidifying and so eliminates the risk — while no source in the corpus attributes a blister on an RC print to drying temperature; the datasheet gives an 85 °C hot-air limit and a warning about glazing, and names no blister

This is the difference between a mechanism with converging evidence and a plausible extension of it. The gas account has a stated mechanism, stated conditions, a stated dry appearance and a product sold on the strength of it. The RC drying account has a real published temperature limit that could be about anything — sticking, curl, cockling — and no source connecting it to blistering. The course states the first as established, offers the second as its own inference and labels it, and leaves the reader able to tell which is which.

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