Re: Clearing chromium (was Quoting Paul Anderson)

Philip Jackson (pjackson@nla.gov.au)
Thu, 30 May 96 18:47:00 PDT

Judy's comments on pigment stain in gum remind me of an earlier discussion
regarding different chemicals for clearing chromium stains. I vaguely
remember sodium bisulphite and potassium metabisulphite being suggested at
the time, but recently came across a new candidate that might be worth
considering. It comes from a dichromated gelatin hologram article by Jeff
Blyth (Applied Optics, 30 (1991) 1602) and consists of a 1% solution of
sodium dithionite.

Sodium dithionite is also known as sodium hydrosulphite Na2S2O4 * 2H2O which
to a non-chemist looks a bit like sodium hyposulphite Na2S2O3 * 5H2O. I have
no idea whether hypo (which is also used as a reducer in chrome dyeing)
could be substituted, or indeed whether it would be as effective as sodium
hydrosulphite, which is used as a chromium removal reagent in water
treatment. It's also supposed to be a photographic developer ingredient, but
I don't recall ever coming across it before. I should also make it clear I
have no idea of how toxic sodium dithionite might be or what effect it might
have on paper or pigments (it was being recommended for clearing glass plate
dichromated gelatin holograms).

Philip Jackson (pjackson@nla.gov.au)