Re: Pyro staining developers

From: Sandy King <sanking@clemson.edu>
Subject: Re: Pyro staining developers
Date: Thu, 20 Nov 2003 17:53:48 -0500

> I read the article below. Good information but I was left somewhat
> confused regarding the difference between sodium metabisulfite and
> potassium metabisulfite. Are these two chemicals interchangeable in
> most formulas? If not, what would be the difference?

I don't think I ever mentioned potassium metabisulfite in that
article. The difference is obviously in the cation part, which is
pretty inert in terms of development process. One practical difference
is that potassium salt is more soluble but also more expensive. For
the amount used in most formulae including yours, the concentration is
well below the solubility limit of the sodium salt so it won't make a
difference, except the cost -- use sodium metabisulfite.

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)