Paper storage fog

Owned by Break/Fix — the room that fogs and the light that is not even, which says the thing that makes this fault diagnosable at all: it is indistinguishable from safelight fog by inspection, and is separated only by processing an unexposed sheet from a fresh unopened packet beside one from the packet in use. Those two controls are the whole of the chemistry that page needs, and their three outcomes decide whether the fault is the material, the room or the developer. It names this entry as carrying the rest. This entry was written earlier from the manufacturers’ storage specifications and from permanence and image deterioration.

What you see

Highlights that are not white and a base that is not clean, on prints made carefully, in a darkroom that passes its fog test, from a negative that prints properly on other paper.

The strongest evidence is comparative and it is worth taking before anything else. A sheet from a different box, exposed and processed identically, comes out clean. That single comparison moves the fault from the room to the material, and this entry is the material half.

Likely causes

1. Warm storage, over months. Heat is the largest single factor and it is cumulative.
2. Damp storage. Kodak are blunt about a damp basement: dampness causes deterioration of films and papers which can result in weak, mottled pictures.
3. Age. ILFORD give MULTIGRADE RC two years in excellent condition when stored as recommended — a figure that is conditional on the storage, not independent of it.
4. Light reaching the packet, from a box opened in the light, a torn foil bag, or a packet left out.

What is happening: the chemistry and physics

Paper fog is base fog on a reflective support, and its causes are the same family. What differs is that on paper the consequence lands where the reader looks first.

Heat moves grains towards developability without light. Every silver halide emulsion carries a distribution of grain sensitivities and a population of latent sub-image centres; warmth over months lets some of them grow past the threshold at which a developer will take them. The result is density where no exposure was given, and on a print that is grey where the paper should be white.

Damp does two things. It carries the chemistry of the emulsion into motion and it feeds mould, and Kodak’s observed outcome — weak, mottled — names both: a general loss of contrast, and unevenness.

Age is the sum of the other two integrated over time, which is why every keeping specification is stated as a period under stated conditions and is meaningless without them.

!The confirming test: two boxes, one exposure

Expose and process a sheet from the suspect box and a sheet from a fresh box in the same session, at the same exposure, in the same developer, and compare their unexposed borders.

• The suspect sheet’s border is greyer: the material is fogged, and no darkroom change will fix it.
• Both borders match: the material is fine and the fault is in the room, the developer or the enlarger.

The second test separates fog from exhausted developer, which is the fault it is most often confused with, because both give grey-looking prints. Develop an unexposed sheet fully. A fogged sheet goes grey. A sheet in an exhausted developer stays white and simply refuses to reach a good black when exposed, which is the developer-exhaustion fault.

Diagnostic questions

• Where has the box lived, at what temperature, for how long? Kodak’s advice is to store paper where it is cool and dry and bring it to the darkroom only when needed.
• Is the darkroom the store? A darkroom is often the warmest and dampest room in the house, and is therefore the wrong cupboard.
• Was the packet resealed? Kodak’s instruction is to return unused paper to its original package, and the foil bag is part of the specification.
• How old is it, and is the date on the box? The unlabelled or undated container discipline applies to materials as well as solutions.
• Does an added restrainer help? If a trace of benzotriazole restores the whites, the fault is fog rather than anything optical — though see the corrective section for why that is a working answer rather than a cure.

Corrective action

Fogged paper does not un-fog. That is the honest headline, and it is the same statement made in elevated fog on a curve: density added uniformly cannot be subtracted selectively.

A restrainer can buy back some of the whites. Part VIII owns the chemistry and benzotriazole is the encyclopaedia entry. It costs paper speed and it shifts image tone, and the course states the trade rather than recommending a dose it has not measured for your paper.

Grade up. A fogged paper has lost contrast at the highlight end; a harder grade or a harder filter restores some of the separation, at the price of the shadow end.

And then buy paper, because everything above is a way of finishing a box rather than a way of printing well.

Prevention

Cool, dry, dark, and in the original packaging, which is what the specification assumes and the only condition under which the keeping figure means anything.

A dehumidifier if the store is a basement, which is Kodak’s own remedy for the location most home darkrooms use.

Buy what you will use. A two-year keeping figure under stated conditions is not a two-year figure in a darkroom that reaches 28 °C in August.