From: Judy Seigel (jseigel@panix.com)
Date: 01/08/02-03:16:56 PM Z
On Tue, 8 Jan 2002, Richard Knoppow wrote:
> >Chrome alum can certainly be used as a hardener and it is used in some stop
> >bath formulae. Since Chromium is a known hazard . . here you might think of
> >the intensifier Mercuric Chloride to get an idea of the hazard of metals . .
> >. you might consider using Potassium Alum instead.
> Formaldehyde produces the greatest hardening of the three, next comes
> chrome alum and then plain alum.
This is an abstract statement which doesn't apply unless the other parts
of the equation are attached... Which is to say the formaldehyde is used
in great dilution for a limited time -- and hardens enough, or too much.
To harden more you could use it stronger or longer, but how much do we
want our gelatin hardened anyway... enough so highlights slide off? (As
they will.)
On the other hand, whoever uses gelatin with no hardening is doing a dumb
thing. Unhardened gelatin takes pigment stain more, washes off more, gets
eaten by bugs MUCH more, and etc. etc. etc.
For what it's worth, I repeat my findings of a test of glyoxal vs.
formaldehyde, of course using my materials:
On the next day the formaldehyde hardened paper still outgassed so
strongly that (even though it had been dried all day outdoors) bringing it
into the studio filled the room with fumes so strong that my eyes & throat
burned & I had to remove it.
Equally important: The gyloxal-hardened paper cleared much more nicely.
What it would have been like a week later, when Mr. F was done gassing,
who knows? I didn't care because I live indoors & having to harden paper
outdoors (often in dead of winter) is a big pain. I've used formaldehyde
indoors, not something I would willingly do again. And CERTAINLY not with
a class unless you want an uprising from the populace at large.
The downside of glyoxal (and DO NOT LISTEN to someone saying which hardens
"better," there is no better in this case because it's use and materials
dependent) is that the working solution doesn't keep well. You should mix
only what you need and prepare a bunch of paper at a time.
The upside (aside from not killing the cat with glyoxal) is that you can
get it. Artcraft has it, and probably others also (tho I think Artcraft
may have the best price)... Recently I learned on this very list that some
sources do still sell formaldehyde, but getting it generally isn't so
easy. (It's used in making crack cocaine was the story I heard, so maybe
you could get some from those quarters no problem. Which also may be why,
I'm told, it gets stolen even from locked cabinets in hospital labs... tho
maybe on second thought that's the gum printers, fresh out of glyoxal.)
> Chrome alum (potassium chromium sulfate) must operate a fairly low pH to
> harden. There are fixer formulas using it. Mostly chrome alum stop baths
> and fixers were used for tropical processing and in some motion picture
I know several gum printers who put the alum in their gelatin & like it
fine. I've planned to try it too, tho I think I feel more comfortable with
the two ingredients controlled separately... So maybe that's not the best
beginner's plan.
In any event, welcome to gum, Clay -- as you can see one of its great
charms in the inspiration to literature...
best,
Judy
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