Mottle revealed only after toning

Owned by Sulfide and Sepia Toning, whose table of the faults that only appear after toning states the general principle this entry is one case of — a toner does not usually cause the faults blamed on it, it develops them — and which spells out what Kodak leave compressed: an over-concentrated stop bath is not one somebody mixed wrongly, it is one that concentrated itself by evaporation in a tray over more than three days or a tank over more than a month. This entry was written earlier from Kodak’s G-23 and Part X’s stop-bath chemistry.

What you see

A print that was even until it was toned. After a selenium or sulfide toner, a patchy unevenness appears in the base — in the paper white and the light tones rather than in the image — and it was not visible before.

The delayed appearance is the whole diagnosis, and it is the reason this entry exists separately from print mottle and uneven toning. Kodak say it in one sentence: the mottle will not be evident until you tone the print with a selenium or sulfide toner.

Likely causes

Kodak give two, and both are the stop bath:

1. An over-concentrated stop bath. Their condition is specific: leave stop bath in a tray for more than three days, or in a tank for more than one month, and evaporation may over-concentrate it.
2. Insufficient agitation of prints, especially during the first few seconds in the stop bath.

To which they add, elsewhere on the same sheet, the two general ones:

3. An exhausted stop bath, named alongside the over-concentrated one.
4. Uneven development, since Kodak require the recommended development temperature and time to obtain uniform image colour.

What is happening: the chemistry and physics

Toning is a differential process, and that is why it acts as a developer for faults. A toner replaces or augments image silver — selenium and sulfide routes both convert metallic silver into a more stable compound with a different colour — and how far it gets in a given time depends on what the emulsion and its base are like locally. A difference too small to see as a density difference becomes visible as a colour difference once the toner has amplified it.

Why the stop bath in particular. A stop bath’s job is to halt development instantly and everywhere, and Part X owns the chemistry: a swing of pH that stops the developing agent working. A bath that is too strong swings it violently, and a print that enters without agitation meets that swing unevenly — the first few seconds are when the whole surface is supposed to be reached at once. Whatever local difference that leaves is in the base, which is exactly where Kodak say the mottle appears.

Kodak do not offer a mechanism for the base mottle itself, and neither does this course. What is sourced is the association and the conditions; the step from “over-concentrated stop plus poor initial agitation” to “visible base mottle after toning” is stated by the manufacturer as an observed cause and is not derived here.

!The confirming test: tone a scrap that never had a print on it

Process a blank sheet — no exposure — through the same developer, the same stop bath and the same fixer, then tone it.

• The blank mottles: the fault is in the processing chemistry, not in the printing, and the stop bath is the first suspect on Kodak’s own list.
• The blank is clean: the unevenness is in the image, which points at development rather than at the stop.

Then change one bath. Mix a fresh stop bath at the recommended dilution and repeat with the same developer and fixer. If the mottle goes, the diagnosis is complete.

And date the tray. Kodak’s own conditions are a matter of days in a tray and a month in a tank; a stop bath with no date on it cannot be assessed against them.

Diagnostic questions

• How old is the stop bath, and has it stood in an open tray? Three days is Kodak’s number for a tray.
• Does the bath have an indicator, and has it turned? ILFOSTOP signals exhaustion by colour, which addresses one of the two failure modes and not the other — an over-concentrated bath is not an exhausted one.
• How is the print put into the stop? Face down in one movement, immediately agitated, is the technique Kodak’s sentence is about.
• Is the mottle in the base or in the image? Base points at the stop bath; image points at development.
• Which toner? Kodak specify selenium and sulfide as the toners that reveal it, which is corroboration when they are what you used.

Corrective action

The toned print cannot be mended. A toner has changed the silver, and the unevenness is now part of the image.

Mix a fresh stop bath at the recommended dilution and re-print. That is the fix, and it is cheap.

Improve the entry technique — slide the print in face down and agitate at once — because that half of the cause costs nothing to remove.

Prevention

Date the stop bath and discard it on Kodak’s schedule, tray or tank.

Do not use an over-concentrated bath, and remember that concentration rises by evaporation without anybody adding anything.

Test-tone a scrap from every session before committing a print you care about. Toning is the last irreversible step in the sequence, and it is the step that shows you every fault the earlier ones left behind.