Residual silver and yellow staining

Owned by Fixer Faults, Washing Faults and the Stains They Leave, which sets this against residual thiosulfate as the fixing half of the pair — silver complexes that never became washable, because the bath was tired or the time short — and warns that material failing both tests has a fixing problem first, since lengthening the wash leaves the actual cause running. This entry was assembled from Break/Fix — the exhausted fixer and permanence and image deterioration.

What you see

A yellowing that was not there when the print dried, strongest in the borders and the highlights.

It is the slow one. It is the reason a fixing experiment needs a three-week wait before it can be read, and it is the most important symptom in the whole fixing set, because a print that looks perfect on the drying rack and yellow at its edges two years later was already faulty on the rack and the fault was invisible by construction.

A toner does in a minute what the air does in years, which is why Kodak’s toning manual is where the clearest published statement of it lives.

Likely causes

1. An exhausted fixer, which leaves the sparingly soluble step-one complex in the paper.
2. Fixing time too short for the material and the bath.
3. A single bath used where two were needed.

What is happening: the chemistry and physics

The white parts of a print are where development reduced almost nothing, so they are where the most undeveloped halide was, so they are where the most silver-thiosulfate complex was formed. If the bath was spent, that complex formed as the sparingly soluble step-one species, in the paper, where — Kodak’s toning manual says it flatly — washing cannot remove it.

It is invisible when it forms. What makes it visible is sulfide, from the air over months, or from a toner in one minute.

2 [Ag(S₂O₃)₂]³⁻ + S²⁻ → Ag₂S + 4 S₂O₃²⁻

The retained complex becoming a stain

So the geography of the stain is a map of where the halide was, and the delay is the time it takes for something to come and find it.

📓Two stains, one word

This is not oxidation stain, which is a brown general stain present from the first day and comes from oxidised developer carried into the fixer.

The timing separates them, and so does the geography — oxidised developer stains generally, retained silver stains where the halide was. One is a developer problem in the fixer; the other is a fixer problem in the paper.

Diagnostic questions

• The sulfide test, which is the published one for prints. ILFORD’s procedure — dissolve 2 g of sodium sulfide in 125 ml of water and dilute 1+9 for use; put a drop on a white area of a print known to be well fixed and thoroughly washed by the two-bath method, blot off the excess, and the barely visible cream tint left is the reference colour for that paper. Any subsequent print showing a yellowing of the test spot is not properly fixed. Prints must be well washed before the test; it is not effective straight from the fixer.
• When did it appear? Late, and in the whites, is this entry.
• Was it toned? A toner converts the retained complex immediately, so a stain that appeared during toning is this fault arriving early rather than a toning fault.
• What was the fixer’s clearing time as a ratio to fresh, and what does the capacity log say?
• Did the material go through one bath or two?

Corrective action

A print whose stain has appeared is not rescuable. It is not a deposit on the surface; it is in the paper.

A print or negative whose stain has not yet appeared, from a batch you now suspect, is rescuable - refix it in fresh fixer and wash it in full, while it is still recent. Refixing converts the retained step-one complex into the step-two complex, which the wash can then remove.

The judgement is real and it is the point of the fault. A mildly under-fixed negative prints perfectly and carries a promise about the future rather than a statement about the present. For a test frame, do not bother. For anything you would be sorry to lose, do, and the cost is fifteen minutes and a litre of fresh fixer. Cheap now, impossible later is the whole economics of permanence.

Prevention

Two-bath fixing for anything you care about, because the rotation exists precisely to ensure that nothing leaves the fixer while the invisible insoluble compound is still in it.

Fix for twice the clearing time, and keep the bath within its published capacity.

Establish the sulfide-test reference tint for each paper you use, once, on a print you know to be correctly processed, and keep it. Without the reference the test has nothing to be compared against.