Re: Autoclaving gum and gelatin

On Sun, 6 Feb 2005, Sandy King wrote:

> As for the change of state, what I refer to is the ability of gelatin to
> absorb water and swell, and when heated, reach a melting point and form a
> colloid, then to set again when allowed to cool. So long as a gelatin
> solution is capable of changing between these two states it should be good
> for both gum bichromate and carbon use, IMHO. If the gelatin looses its

"Should !" That's like "probably" or "arguably" and the other empty
calories that infest the canon.

Not to mention that you are in error anyway (and I break my promise not to
continue this thread, as, from the kindness of my heart I give you info
you clearly lack). That's error BESIDES the "seems-logical disease," in
which you extrapolate from theory (I suspect of your own
choosing/devising) rather than observation.

There is also the fact that I have taken gelled gelatin out of the
refrigerator, that is, gelatin in a state of gel that was, alas, rotten
(as could be told from its stink, not its "state"), and, refusing to bow
to the evidence of my nose, coated a paper with it. The print failed
miserably. Not expecting to be called to the witness stand, I made no
record of details, except that I threw out both the gelatin and the failed
print (not knowing at the time what I learned subsequently, that a new
layer of "good" gelatin would probably rescue it -- another item I learned
from students).

I cordially invite you, however, to repeat the "experiment" yourself --
about a week in a refrigerator as funky as ours should suffice.

While you're at it, you can try hosing a developing gum print with
scalding water and note time, temperature, pressure and results with, say,
3 different emulsions and exposures. You should also enact the business
about the boiling or the overheating you've been speaking of -- and see
the effects for yourself.

You could add to the sum total of human knowledge and/or learn that
behavior of a gum print vis-a-vis gelatin is goosier than that of
carbon... Of course the usual variables (paper, gelatin, hardener, water,
rH, etc.) would affect outcome & should be controlled for.

> ability to set, either from very extreme temperatures, being held at a high
> temperature for a long time, or from repeated cycles of heating and cooling,
> it will lose its ability to set. This will make it useless for both carbon
> and gum bichromate.

Again, with theory not firmly connected to the problem, let alone direct
observation, you are in Assertion City. A gel that would no longer "set"
could still coat a paper and dry enough in the air to be printed upon,
though if it were applied directly from boiling, with no attempt to let it
gel -- who's to know? That is, gelling or not gelling enters the
calculation only if you're testing for it.

But go ahead, be my guest...test. Of course a proper test, controlling for
variables of gelatin, temperature, degree and frequency of heating, etc.,
could send students (ipods and all) into deep sleep.

I prefer to simply warn them (and others) about heating the gelatin above
140 F. Something along the lines of my earlier exegesis Ryuji so kindly
posted today. I have found that, barring inattention and hexed hot & cold
water lines, it generally does the trick.

Judy
Received on Tue Feb 8 04:59:54 2005