Re: Chrome Alum Gelatin hardener

On Tue, 10 Feb 2004, Ryuji Suzuki wrote:
> Indeed, this is why the focus of aldehyde hardeners in literature in
> 1970's shifted to the mechanism of hardening with glutaraldehyde,
> because this mechanism is different from that of formaldehyde or
> glyoxal. You really need to see literature from late 70's to get any
> details on glutaraldehyde hardening mechanism.
CUT
>
> For silver gelatin process, formaldehyde has more direct disadvantage
> like tendency to fog, reduce speed, or both, especially in fast
> emulsions. I wouldn't use it.

To apply info pertaining to silver gelatin (however impeccable it may be)
to gum printing is at the very least apples and oranges... And even apples
vary tremendously.

Before my first tests of glyoxal, I did consult with chem dept at Pratt,
the prof shared the lit with me, which for whatever reason gave
glutaraldehyde as a near death experience... But there were other aspects
(which I forget now, it having been some 6 or so years ago) that suggested
to both of us that the g-aldehyde wouldn't work as well.

In any event, I tested formaldehyde against the gyloxal and found that on
every count the glyoxal was better... My test consisted of gelatin VAT
sizing (one-side sizing for gum is a mistake anyway, because the paper
will curl, and vat sizing when you do it right is better & easier) paper
with 3% knox gelatin, drying, then hardening, then several 21-step prints
a day later.

The glyoxal-hardened strips nearly ALL cleared better, that is of the
several colors & brands I tried.

I realized at the time that the formaldehyde hardened strips might have
done better later... but that wasn't the proposition, which was to find a
substitute for formaldehyde now unavailable generally & VERY unpleasant to
use (especially with a class, but in one's home awful too.) I should add
that no matter what they CLAIM about reasons for closing off formaldehyde,
the real reason (I'm given to understand) is that it's used to make crack
cocaine, or one of those controlled substances.

In any event, even a day later the formaldehyde was outgassing so strongly
(after drying outdoors) that I had to remove it from the room. The
glyoxal was just scarcely noticeable.

But I'll also add that yellowing when the glyoxal is IN the gelatin
doesn't necessarily mean yellowing when used as a final rinse and then
itself rinsed off. I have yet to see or hear about glyoxal yellowing when
rinsed after the bath... The hardener in the gelatin is all kinds of
complication IMO-- and cannot be used later, which is an issue when your
batch is nearly a gallon.

As for adding a plasticizer to the glutaraldehyde -- even if it applied to
use in gum printing... another complication in a process that already
presents more variables than the mind can grasp... I'd rather use the
paper unsized than add more on that level...

Oh, and as far as the effects of HEAT on links of gelatin hardened with
glyoxal vs. glutaraldehyde-- if the water is too hot during or after
gelatin sizing, the size coat is spoiled anyway, and the print will
speckle... irrespective of the hardener.

Judy
Received on Tue Feb 10 16:36:11 2004