Oxidation stain

Owned by Fixer Faults, Washing Faults and the Stains They Leave, which keeps the appearance here and sends the cause to Chemistry in the Bottle, where oxidised developing agents are shown to be coloured and to be deposited along with the silver. That page also names the trap this entry must not fall into: the stain of a pyrogallol or catechol developer is wanted, is image-wise, and is told from this one by whether it covers the rebate. This entry was assembled from Break/Fix — the exhausted fixer, from the section on the two stains that share a word.

What you see

A brown or yellow-brown general stain, present from the first day. It is there when the print dries. It is general rather than local, and it does not favour the highlights.

That timing and that geography are the whole of the discrimination, because there is a second stain that shares the word and behaves in the opposite way - residual silver staining, which appears later and is strongest in the borders and highlights.

Likely causes

1. Material moved from developer to fixer with little or no rinsing.
2. A fixer whose sulfite has been used up and whose acid has been neutralised — which is to say an exhausted bath.
3. Developer left standing on the surface of the material before it reached the next bath.

What is happening: the chemistry and physics

Kodak’s 1928 primer sets out the whole chain in one paragraph. Material goes from developer to fixer with little rinsing; the developer oxidises in the bath; the bath turns brown; and it stains negatives and prints.

The sulfite is what prevents it. A fixer’s sulfite is there to reduce the oxidation products of the developing agent back before they can attach themselves to the gelatin, and an exhausted bath is one whose sulfite has been spent and whose acid has been neutralised by the alkali carried in with the developer.

So this fault is a developer problem happening in the fixer, which is why it is not cured by fixing longer and why it does not respond to anything done to the developer alone.

!Two stains, one word, and the two questions that separate them

When did it appear? This one was there when the print was dry. The other appears weeks or years later — and if you photographed your prints when you made them, which you should have, the two are trivially separable.

Where is it strongest? This one is general. The other is strongest in the whitest parts, because that is where the most undeveloped halide was.

One is a developer problem in the fixer. The other is a fixer problem in the paper.

Diagnostic questions

• Was the stain there on day one? A photograph of the print on the drying rack answers this and nothing else does reliably.
• Is it general, or strongest in the borders and highlights?
• What colour is the fixer? A bath that has turned brown is carrying oxidised developer, which is both a symptom and a cause.
• Was there a rinse or a stop bath between the developer and the fixer?
• How much work has the bath done? The sulfite reserve is finite and it is spent by carry-over as well as by fixing.

Corrective action

Not rescuable. The stain is not a deposit on the surface; it is in the paper.

The bath is another matter — discard it, route it as silver-bearing waste, and mix fresh.

Prevention

Rinse before the fixer, or use a stop bath. The stop bath is better because it stops development as well as removing the carry-over, and it is the single control that prevents this fault and dichroic fog together.

Do not let material stand in air between baths. Move it, drained, straight through.

Keep the fixer within its capacity, and test it on a schedule. A bath whose sulfite reserve has gone is a bath that will stain whatever is put in it next.