Re: yellow gelatin

From: "Christina Z. Anderson" <zphoto@bellsouth.net>
Subject: Re: yellow gelatin
Date: Tue, 23 Mar 2004 09:01:43 -0500

> the old glyoxal is concentrated urine yellow, the gelatin is
> Knox, and when I mix the glyoxal in the gelatin (25ml tho) it is
> definitely yellow.

Knox makes many kinds of gelatin... If you are talking about food
grade gelatin, it tends to be more yellowish color, lower clarity and
low Bloom strength. That means you need more hardener...

> I have a pH meter and I can't find it (amazing that that is the
> case, since I have all gum stuff in one measely room) but I'll have
> to measure my water.

That's no good... pH probe should be kept wet in a solution of KCl in
slightly acidic environment (a bit of boric acid will do). Otherwise
the reference junction dries up and the glass membrane gets damaged
over time.

> Speaking of dichromate buildup, I remember Sil saying there was no
> need to wash residual dichromate out of the print--it would not damage its
> archivalness. With the lower dilution dichromate this is no longer much of
> a problem for me, but I want to make sure that this is the case, that
> dichromates do not "age" in a print, if left behind in trace amounts? I was
> getting a batch of prints ready to frame and I ended up clearing them just
> to be sure they were completely archival because I didn't want to chance it.
> What do you all think?

I think dichromate is used in far excess amount so there should be
plenty of them left in unless you do very careful washing. But if you
really worry, I think it should be a simple matter to chemically or
physically decompose residual dichromate into more stable form after
washing. If you reduce Cr(6) to Cr(3) you'll get additional potential
benefit of further hardening the gum. If there's any undesirable
reaction by keeping small amount of dichromate, I'd look into what'd
happen to the pigment upon future decomposition of dichromate.

By the way, the glutaraldehyde you have is at least 2 years old.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)