From: Judy Seigel (jseigel@panix.com)
Date: 02/27/03-08:31:15 PM Z
On Wed, 26 Feb 2003, Christina Z. Anderson wrote:
> So, in gum research today, re: glyoxal yellowing, I came across the
> statement Judy made that an alkali added to glyoxal turned it orange. Is it
> possible that the yellow stain that happens sometime with glyoxal is a mild
> alkali in the paper that has been sized with glyoxal and it affects it
> sitting in the drawer, and this is this "orange" tint diluted by the paper
> base white? Maybe buffered papers might yellow the glyoxal just sitting
> there?
That's a brilliant thought Chris.... it would go along with Liam's point
that most modern papers are buffered.... On the other hand, my own finding
is that I got "yellowing" only along the edge where there was a buildup of
*gelatin.*
And incidentally, bicarbonate of soda didn't yellow the glyoxal, for what
that's worth -- but I solved the entire problem by just skipping any
alkali in the hardener. I never felt the lack of it & frankly it has
entered my mind that we have only theoretical reasons (linking the
gelatin) why it's useful, I've never seen or heard of any tests showing
that the gelatin really held better with the alkali (and so another
complication bites the dust).
I'm going to try that K-6 anyway.... as it happens I have a bottle of it
on the shelf (like just about everything else... that shelf is going to
crash down to china -- look out below). But I notice that mine is *gloss.*
Who was it said they use K-6? Is gloss OK?
> Also, since alkaline conditions make dichromates work more slowly (hence
> adding ammonia to a dichromate to slow down printing, or slow down dark
> reaction to enable storage of paper) is the reason different gelatins have
I did a whole lot of tests of that very thing, when I was young and frisky
about 5 years ago...my ultimate conclusion was that that was entirely
inconclusive, that weakening the concentration or lowering the exposure
did exactly the same thing -- or so nearly as could be called "exact" for
all practical purposes.
For a while I was convinced that adding ammonia to the emulsion DID make
it keep better, but then I never could prove it -- and dropped it....
just another variable, and let's face it, mixing the emulsion is a matter
of a minute -- and one less variable.
J.
> different printing speeds because some are more alkaline than others? Or is
> it just the viscosity? I mean, it seems acid (lemon juice) speeds up
> emulsion and ammonia slows it down so I was just wondering...
>
> That's my musings for the day.
> Chris
> PS my white gouache on cyanotype printed with a positive worked fine, but it
> was, as Keith said earlier, sort of anemic and grey. It did not seem to
> bleach the cyano as much as I expected, either. The positive did much better
> in white on cyano than the negative.
>
>
>
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