Re: Sodium Bisulfite

Darryl Gage wrote: (August 21)
>
> After clearing a 2 or 3 gum prints, is the sodium bisulfite solution
> storable for later use or should I just dump it and make a new solution
> when needed? Thanks.
>

I'll bet you all thought we had pretty much beaten this subject to
death, but I find that I have another thing to say about it after all.

When Darryl asked this question, I answered that it isn't necessary to
dump it out and use it every time, but that it can be re-used, and that
in fact I had once used a gallon of it for 3 or 4 years before it lost
its ability to clear effectively.

I think I was careful to say that that gallon cleared a rather small
number of prints during the 3 or 4 years, and I should add that the
gallon jug was full and stayed full, so there wasn't air continually
oxidizing the sulfite. And I should also add, to be very clear, that
even the small number of prints that I cleared in that time were not
heavily stained, as evidenced by the fact that throughout the effective
re-use of the sodium bisulfite, it stayed clear and colorless.

Today, for a project I won't bother to describe here, related to my
ongoing research into the chemistry of the gum process, I've been
exposing unpigmented dichromated gum in direct sun until the dichromate
turns dark brown, and then after water development, clearing it in a
sulfite bath until the hardened gum is colorless and transparent. I
found that in the process of clearing a strong stain like this, the
bisulfite bath turned quite blue, the color of chrome alum (which makes
sense given what someone told me about the clearing being a function of
chromium pairing with sulfate). When it turned blue with the first
print, I didn't re-use it but dumped it out and used fresh for the next
print and so forth, and would certainly recommend the same action for
anyone else who finds themselves with blue clearing agent on their
hands.

Hope that's clearer,
Katharine
Received on Tue Aug 31 20:26:35 2004