Fixer contaminated by developer

Owned by chemistry in the bottle. The reverse direction — fixer into the developer — is far more damaging and far less common.

What you see

Nothing, at first. This contamination is unavoidable in principle, because every piece of material carries some developer with it, and the fault is a matter of degree.

What you eventually see is one or more of three separate faults, and their appearance is the diagnosis:

1. A fixer that dies early — its clearing time rising well before the published capacity has been used.
2. Dichroic fog — a veil that is greenish by reflection and reddish by transmission.
3. Hardener sludge in an alum bath — a white gelatinous precipitate.

And a fourth on hangers, which Kodak’s 1928 primer records: a mottled image, where “in the absence of thorough rinsing and agitation, development continues locally during the first few minutes of fixing and in these spots the image has greater density”.

Likely causes

1. No stop bath and no rinse between developer and fixer.
2. A water rinse used too long without changing.
3. Printing rather than film processing. The primer is specific: “when fixing prints, a relatively large proportion of the developer is carried over to the fixing bath (unless a water or acid rinse bath has been used)”. A print carries a soaked paper base as well as an emulsion.
4. Tongs or hands moving directly from the developer tray to the fixer.

What is happening: the chemistry and physics

An acid fixing bath is acid for reasons, and carried-over alkaline developer neutralises the acid. Everything on this page follows from that one sentence.

It shortens the bath’s life. ILFORD’s own account of exhaustion names three mechanisms and this is one of them: an unreplenished bath “is eventually exhausted by the build up of silver and halides in it and the action of solutions carried over from the preceding baths that can cause some dilution and the pH to be raised”.

It invites dichroic fog. Kodak’s primer names a bath that “does not contain acid” as one of the two conditions under which dichroic fog appears, and states that it never occurs “if the film is rinsed before fixing”. Wall’s 1912 dictionary reports Lumière and Seyewetz reaching the same conclusion from the other direction: its formation is favoured “by the presence in the fixing bath of developer, hence the desirability of washing the plate between developing and fixing”. Two sources, thirteen years apart, both naming the rinse.

It precipitates the hardener. In an alum bath, the acid is what keeps the aluminium and the sulphite apart. Neutralise it and they combine into aluminium sulphite sludge.

And it makes gas. A carbonate developer carried into an acid fixer produces carbon dioxide, which is the blister mechanism.

!This is what a stop bath is for, and the makers say so in those words

ILFORD’s description of ILFOSTOP is a list of exactly the faults above: it stops development immediately, neutralises the developer “to help maintain the activity of the fixer bath”, and “helps to maintain the activity and prolong the life of the fixer solution by reducing carry over of excess developer (alkaline) into the fixer bath (acidic)”.

The specification is small: 1+19, ten seconds, at 20 °C, for film and paper alike.

And where a stop bath is not used, ILFORD are candid about the cost: a water bath can be substituted, but “using a water bath instead of a stop bath increases the risk of seeing processing related marks and stains”, so “the water bath must be completely changed at very frequent intervals”, and “fewer fixing problems will be seen if the fixer’s activity is monitored”.

Ten seconds and a fifth of a litre of dilute citric acid buys the fixer’s life, the absence of dichroic fog, the absence of sludge and the absence of gas blisters. It is the best-value step in the whole process.

Diagnostic questions

• Is there a stop bath or a rinse between the developer and the fixer? If not, this diagnosis is live for every fault on this page.
• How old is the rinse water? A tray of water used for twenty prints is a weak developer.
• Is the fixer’s clearing time rising faster than the running total suggests it should? That is the early warning, and it needs the fresh clearing time to have been measured.
• Is it prints, or film? Prints carry far more.
• Has the fixer’s pH risen? ILFORD’s rapid fixer publishes pH 5.0–5.5 at both dilutions when fresh, and their sheet contemplates the pH rising when no stop bath is used.
• Is there a white gelatinous sludge? An alum bath losing its acid.
• Is there a two-coloured veil? Dichroic fog, and it is the expensive outcome.
• Are the tongs shared between the developer and the fixer trays?

Corrective action

For the bath: where a stop bath is not used and the pH has risen, ILFORD give an explicit remedy — add a few drops of 50 per cent acetic acid gradually, with stirring. That restores the acidity; it does not restore capacity that has already been spent, and it is a correction rather than a rescue. Where the clearing time has already doubled, discard.

For the material: nothing. Dichroic fog, sludge and blisters are all permanent, and the mottle from continued development in the fixer has already happened.

Prevention

Use a stop bath. ILFOSTOP at 1+19 for ten seconds, or the equivalent from any maker.

Where you use water instead, change it very frequently — ILFORD’s own words — and monitor the fixer.

Rinse prints properly, because they carry the most; a print lifted straight from the developer into the fixer is the worst case in a home darkroom.

One tong per tray.

Keep a running total and a clearing-time record on the fixer, so that a bath dying early is visible as a number rather than as a surprise. Exhausted fixer has the rule.

And note that the two contamination directions want opposite habits. Developer into fixer is prevented by a bath in between; fixer into developer is prevented by never letting them meet at all. The stop bath handles the first, and dedicated vessels handle the second.