Control chart: developer exhaustion

Lifted from process control with control strips, whose “four causes, four signatures” section is the source of the discriminators below, and from the exhausted developer entry, which is the same fault seen in the bottle rather than on the plot.

What you see

A chart that falls, over runs rather than in one run. Kodak’s definition of a trend is four to eight points climbing or falling in a row; of a level shift, four to eight consecutive points on one side of aim. Exhaustion produces the first and a new bottle produces the second.

Two exhaustions produce two shapes, and telling them apart is the point of this entry.

Likely causes

1. Bromide accumulation in a reused bath.
2. Aerial oxidation of the stock in a part-filled bottle.
3. A reuse compensation too small for your subjects.
4. Normal seasoning of a replenished system, which looks alarming and is not a fault.

What is happening: the chemistry and physics

Bromide accumulation. ILFORD say it in one sentence — each film processed releases halides and other by-products that act as a restrainer on the development of subsequent films — and then quantify the remedy: increase development time by 10 per cent for each successive film through a litre of stock ID-11, up to ten films. Part VIII owns the mechanism: bromide suppresses development, and it suppresses it hardest where there is least silver to develop.

Signature: speed down, fog down, contrast down last and least. Fog falling as speed falls is the fingerprint, because a restrainer restrains the unexposed grains most of all — which is why bromide is in developers on purpose.

Aerial oxidation. A developer in a part-filled bottle is a developer in contact with air, and the manufacturers price it exactly. Kodak give D-76 stock six months full and two months half-filled, with the explanation in one clause: partially filled bottles allow some oxidation. ILFORD are stricter for ID-11 — six months full, one month half-full, four months in a deep tank with a floating lid and one without. Part VIII owns sulfite’s role and measured the effect.

Signature: contrast down, speed down with it, fog roughly unchanged or slightly down. Kodak’s own troubleshooting chart carries the first two against the cause “developer or replenisher too old or oxidised”. The fog half of that sentence is the course’s inference from the mechanism rather than a manufacturer’s figure, and it is the weakest line in this entry — which is why the confirming test below is the bottle’s date and headspace rather than the fog row.

!The confirming test: replace one thing and see whether the chart returns

A point beyond the control limit, confirmed by a second strip, that returns to aim when the bath is replaced and nothing else is changed. That last clause is the whole of it.

Replacing the developer and the fixer and the stop bath together on the same afternoon tells you that something was wrong. Replacing one of them tells you which.

And the discriminator between the two exhaustions is the fog row, backed by the bottle. Fog falling with speed is bromide. Fog flat with contrast falling is oxidation, and the bottle’s date and headspace are the evidence that settles it, because the fog inference is weaker than the keeping figures.

Diagnostic questions

• What are you running: one-shot, compensated reuse, or replenishment? Each produces a differently shaped normal chart, and knowing which you are on is a prerequisite for reading your own plot.
• How many films through this litre, and did you apply the compensation? ILFORD’s own caveat is that the 10 per cent figure can only be an approximation, because a roll of night shots consumes almost no developing agent and a roll of beach scenes consumes a great deal. The chart measures whether your guess was right.
• When was the bottle mixed, and how full is it now? Two numbers, and they settle the oxidation question faster than any strip.
• Is this actually seasoning? Kodak record that some systems are formulated so a fresh solution gives a higher speed than a properly seasoned one, and name D-76 with Replenisher D-76R among them. A declining speed after a fresh mix is normal there and stops of its own accord. Chasing it is over-control.
• Did anything else change on that date? A batch crossover, a new fixer, a warm day. The annotations are what make the chart diagnostic.

Corrective action

Replace the bath, one thing at a time, and re-read. That is both the fix and the confirmation.

If it is bromide and you intend to keep reusing, raise the compensation to fit your own subjects rather than the published table, which is what the chart is for.

If it is oxidation, change the storage rather than the schedule. A full bottle keeps six times as long as a half-empty one on ILFORD’s own figures, and decanting into smaller bottles is free.

Note that the replenishment route is not open for everything: HARMAN discontinued the 2.5 litre ILFORD ID-11 Replenisher pack in September 2012, ID-11 itself unaffected, so a British ID-11 user has one-shot and compensated reuse and not this.

Prevention

Process one-shot. It removes both working-bath signatures at a stroke: no bromide can accumulate in a bath used once, and no bath sits in air long enough to oxidise. What remains is the stock ageing far more slowly in its bottle, so a one-shot chart should be flat — which makes any trend on it a real signal rather than a bookkeeping artefact.

Date every bottle and record the headspace, which is what the labelling SOP asks for and what the unlabelled or undated container entry exists to prevent.

Annotate the chart with fresh mixes, so a level shift on the day of a new bottle reads as an event rather than a mystery.