Round purple spots from air bubbles trapped in the fixer

Owned by Sulfide and Sepia Toning, whose table of post-toning faults records that Kodak give the cause and not the mechanism, and offers the same reading this entry does — a disc the fixer never reached, invisible on a washed print until a toner meets what is still in it. The two Part XX labs carry it into practice from their own troubleshooting sections. This entry was written earlier from Kodak’s G-23 and Part XI’s fixing chemistry.

What you see

Round purple marks, roughly the size of an air bubble, appearing after selenium or sulfide toning on a print that looked clean before. They are circular because bubbles are, and they sit where prints touched each other or where a print met the surface of the bath.

The delay is the diagnostic. Nothing is visible until the toner goes on, which is the same delayed verdict as mottle revealed after toning and a different cause.

Likely causes

Kodak’s own list, in their order:

1. Air bubbles trapped between or under prints during fixing, which they give as the specific example.
2. Prints sticking together in the tray.
3. Prints floating on the surface of the fixer, so one face is not in the bath at all.
4. Insufficient agitation, which is the condition all three of the above depend on.

What is happening: the chemistry and physics

A bubble is a place where fixing did not happen. Wherever air sits against the emulsion, no fixer reaches it, and Part XI’s account of fixing says exactly what that costs: unfixed silver halide stays in the paper, and the complexes that a spent bath leaves behind stay with it.

And residual silver is what a toner finds. Kodak state the general rule on the same sheet: an exhausted fixing bath contains insoluble silver compounds that remain in prints, cannot be washed out completely, and when they come into contact with a toner form a dark yellow stain, especially noticeable in borders and highlights. A bubble produces the same condition locally rather than globally, in a circle rather than at the edges — and Kodak record the resulting mark as round and purple in selenium and sulfide toners rather than yellow.

The course reports that colour difference as Kodak state it and does not explain it. What it can say with confidence is the structure of the fault: a region that was not fixed, in a print that was, revealed by a reagent that reacts with what was left there.

!The confirming test: shape, position and the untoned control

Look at the shape and where it sits. Round marks, sharply bounded, some of them cut off in an arc where two prints overlapped, are air. Diffuse marks along the borders are a spent fixer instead, on Kodak’s own description of a dark yellow stain in borders and highlights.

Then tone a control. Process a second print in the same session, fixing it singly, face up, agitated continuously, and tone it alongside. A clean control with a spotted twin makes the diagnosis without any further test, because the only variable was how the prints sat in the bath.

And run a residual silver test on a scrap. It answers the general question — is this fixer leaving silver behind — which decides whether you have a handling fault or a bath fault.

Diagnostic questions

• How many prints were in the fixer at once? Kodak’s remedy is agitation and separation, and both fail under crowding.
• Were any floating? A print floating on the surface is fixing on one side.
• Do the marks pair up between prints? Two prints face to face share a bubble and share its mark.
• How old is the fixer? A tired bath makes every one of these faults worse, and the clearing-time test is the course’s measurement of it.
• Was a hardening fixer used? Kodak recommend against a hardening fixer for prints intended for toning, because it makes the emulsion less receptive to the toner — a separate fault that can look like uneven toning.

Corrective action

The spots are permanent. They are in the image, and a toner has finished the job.

Re-print, and fix one print at a time — or in a tray with continuous agitation and prints kept apart — until the fault is gone.

Use two-bath fixing, which Kodak recommend for prints intended for toning, and which the course already teaches as a rotation.

Prevention

Immerse, do not slide. Push each print under quickly and completely, face up, and keep it moving for the first thirty seconds, which is when a bubble either escapes or sets.

Interleave rather than stack. A pile of prints in a tray is a pile of trapped air.

Fix within the bath’s capacity and test it, because a bath at the end of its life turns a small handling error into a visible one.