Sodium metabisulphite for polysulphide toner 'stop bath'

[imyself]

Hi everyone,
I've got a 50 'ccm' bottle of unopened viradon toner that's at least 30-40 years old , based on the appearance of the bottle, that I thought I'd use to see if it's still any good. I'm following Tim Rudman's suggestions for dilution ( 1:50 ) and duration ( up to ten minutes ) for use on FB neutral tone paper ( kentmere fineprint VC ). So far so good! He recommends ( so did AGFA, apparently ) the use of a 10% sodium SULFITE ' stop bath' to bring the toning to an abrupt halt. Problem is I've got beer home brew sodium metabisulphite powder on hand and cannot find a source of sub industrial quantities of sodium SULFITE. I've read about the interchangeability of these agents on other posts in this forum but they all related to developer formulae, but what about for this specific indication? Can I just dissolve 100 g of metabisulphite in 1000 ml of water and get on with it? If so, how long could I store the metabisulphite solution for future use? How long would the toner solution last?
regards
Adam

 

[Rudeofus]

There is a profound difference between Metabisulfite and Sulfite: Metabisulfite is quite acidic whereas Sulfite is alkaline. The difference will matter a lot, because an acidic 'stop bath' can and will release (very toxic) H2S. You did not indicate where you are located, but there are plenty of sources in North America and in Europe (and most likely everywhere else) where you can cheaply get small amounts of Sodium Sulfite.

Sulfur toner is one of these things where you don't randomly replace compounds unless you know very well what you are doing!