Re: Clearing Gum Bichromates
s carl king (sanking@hubcap.clemson.edu)
Fri, 12 Jan 1996 19:07:47 -0500 (EST)
> >
> >Another thing I have observed is that you must renew sodium bisulfite
> >on a regular basis. If old or exhausted sodium bisulfite is used
> >to clear papers it will stain the paper blue. This has happened to me
>
> That is new to me. Never heard tell of that. It must take quite sometime
> before it gets to that point?
>
I have seen this happen on at least 3-4 occassions. Initially I was
very curious to see if there was anything in the literature about
it because I very desperately wanted to reverse the effect (since it
resulted in the ruining of some farily large carbros -- 14X19".
I tried to eliminate the blue stain with solutions of sulfuric acid,
chromic acid, boric acid, formalin, succinic acid, etc. etc., but the
end result was that I had to throw the prints away because they
were essentially ruined. As I mentioned earlier, this definitely
happened with papers sized with gelatin and hardened with chrome
alum, and I think one of the papers was also sized with formalin.
And no, as a I recall, the sodium bisulfite was not all that old.\
As best I can recall, a 1.5 liter bottle had been previously used
to clear about 5-6 14X19" prints when the blue staining first
took place.
I know the solution to this problem. Don't overuse sodium bisulfite
to clear dichromate. Still, if anyone has any idea of the chemistry
involved in this happening I would like to hear form you.
Sandy King
Sanking@hubcap.clemson.edu
> >with both Fabriano and Rives papers hardened with chrome alum, and
> >I believe (though not positive) also with formalin.
>
>
> Luis
>
> >Sandy King
> >Sanking@hubcap.clemson.edu
>
>
>