Role of Sodium Metabisulfite in Washing Aid ?

[Ken Lee]

What is the role of Sodium Metabisulfite in this formula for Washing Aid (http://www.digitaltruth.com/techdata/washaid.php) ?

Water 750 ml
Sodium Sulfite (anhydrous) 100 g
Sodium Metabisulfite 25 g
Cold water to make 1L

[Tom Hoskinson]

The Sodium Metabisulfite acts as a buffer for the Sodium Sulfite.

[Ken Lee]

Sounds like it is there to promote longer shelf-life, no ?

So if I were to mix up and use some fresh solution, using only Sodium Sulfite - and then toss it - would there be no need for the buffering agent ?

[Mark Sampson]

To quote from David Vestal's "The Art of B&W Enlarging";
"A test done using home-mixed 2-percent sodium sulfite solution as the washing aid suggests that it's about 80 percent as effective as Kodak Hypo Clearing Agent; a longer wash should get the prints as clean."

[lee\c]

Ken,

I have used just sod sulfite for many years as a subsitute for HCA. I always toss it after the darkroom session. It is too cheap to save and risk it not working.

lee\c