Over-fixing

Owned by fixer faults, washing faults and the stains they leave. Its opposite is under-fixing, and the two are separated by the record rather than by the appearance.

What you see

On a print: the delicate light tones flatten and go, so a portrait’s highlight modelling disappears and a white becomes blank; and the deepest black is very slightly less deep than it should be. The print looks “thin” in a way that more exposure does not correct, because more exposure just puts more silver in to be dissolved. ILFORD note a further symptom on their variable-contrast papers: long fixing times “will affect the image colour”.

On film: a general loss of density, most obvious in the thinnest parts, on a negative that is otherwise correctly processed.

There is nothing dramatic to see. That is what makes this fault persist for years in a darkroom run by somebody careful.

Likely causes

1. Fixing paper for the film time. By a wide margin the commonest, and the origin is caution rather than carelessness.
2. Leaving prints in the fixer while the next negative is set up.
3. Using a film dilution on paper, which changes the correct time as well as the strength.
4. A “holding bath” of fixer used as a place to keep prints during a session.

What is happening: the chemistry and physics

A fixer dissolves silver halide by complexing the silver with thiosulfate. It is far better at that than at attacking metallic silver — that is what makes fixing possible at all — but the difference is one of rate, not of kind. Given long enough, the image goes too.

Why the highlights go first is a matter of size, and it is worth working through because it explains why the fault looks the way it does.

In a print’s lightest tones, the developed silver is present as the smallest and fewest deposits. A given rate of dissolution removes silver from the exposed surface of a deposit, so it takes a much larger fraction of a small deposit than of a large one — and a deposit small enough disappears entirely, taking that tone with it. In the blacks, where silver is piled deep, the same time removes a proportionally trivial amount.

So over-fixing is a contrast-changing fault as well as a density-losing one: it lifts the light end while barely touching the dark end, which is why the print reads as flat and lifeless rather than simply pale.

!Film time and paper time are different numbers, not a range

ILFORD RAPID FIXER at 20 °C with fresh fixer:

Material	Dilution	Time
General-purpose film	1+4	2–5 minutes
RC paper	1+4	30 seconds
RC paper	1+9	1 minute
FB paper	1+4	1 minute
FB paper	1+9	2 minutes

Fibre paper at 1+4 gets one minute. Film at the same dilution gets two to five. A printer who fixes prints for the film time is over-fixing them by a factor of two to five, every print, on purpose.

ILFORD state the consequence in their own words and give it a name: “there is no benefit in extending fixation beyond the recommended time; some loss of print quality might be seen when long fixing times are given due to image etching.”

And there is a second cost, which is the one that outlives the print. ILFORD’s optimum-permanence section asks you not to exceed the fixer’s capacity and not to extend the fixing time, because both make washing more difficult. A long fixation loads the material with more thiosulfate and more dissolved silver to be removed, so over-fixing does not merely etch the image — it sets up residual thiosulfate and residual silver as well.

Diagnostic questions

• What is the fixing time in the record, against the published time for that material at that dilution? This settles most cases without looking at the print at all.
• Are the highlights losing detail while the blacks are nearly right? That is the size argument above, and it is the appearance-side confirmation.
• Is the maximum black slightly below the paper’s published figure? ILFORD publish 2.15 for MULTIGRADE RC DELUXE; Foma publish 2.1 for FOMABROM glossy and 2.0 for FOMATONE glossy.
• Did the prints sit in the fixer while you did something else? The commonest way the time doubles without anyone deciding to double it.
• Has the image colour changed on a variable-contrast paper? ILFORD name it as a symptom of long fixation in its own right.
• Is the fault present on prints from a session where the fixer was fresh? Freshness does not protect against this: a fresh bath etches faster, not slower.

Corrective action

None. The silver has left the print, and nothing puts it back.

Make the print again at the correct fixing time. The negative is unaffected — unless the negative itself was over-fixed, which is a separate diagnosis with the same answer.

Prevention

Write the fixing time on the fixer bottle, per material. Film, RC, FB, at your dilution, in seconds and minutes. This one label prevents the fault permanently, and it is the reason the fault is worth an entry: it is not a skill problem, it is a lookup problem.

Use a timer for the fixer, not just for the developer. A print sitting in the fixer “for a moment” is where the extra minutes come from.

Do not use the fixer as a holding bath. Prints waiting for a wash go in a tray of water, not in the fixer.

And accept the manufacturer’s number rather than adding a margin to it. The instinct to be safe is what causes this fault. The safe direction here is down, not up — provided the bath is within its capacity and the time is measured, which is the exhausted fixer entry’s subject.