Fixer Sulphite Level for PMK

[Josef Guay]

I ran out of TF-4 the other day so I mixed up a batch of sodium thiosulfate with ammonium chloride to speed up the fixing process. The fixer worked well on paper and I would like to use the same fixer for film.

Most recipes that I have found for sodium thiosulfate fixers have 15 grams per liter of sodium sulfite. The few ammonium thiosulfate seem to have lower levels of sulfite.

Should I lower the level the sulfite level so that I don't weaken the staining action of the PMK?

 

[john_s]

I've read that minimal sulfite is better for the stain, but a certain amount is required if the fixer is to be reused. Otherwise it will deteriorate very quickly. For one-shot use, you could leave it out.

For paper, some sulfite is recommended to preserve the thiosulate. It's harder to detect insufficient fixing with paper.