Re: Gelatin hardening question

From: "Christina Z. Anderson" <zphoto@uslink.net>
Subject: Re: Gelatin hardening question
Date: Thu, 15 Jul 2004 22:12:24 -0500

> What may be helpful, though, is a **comparison** of the toxic
> effects of all four--chrome alum, formaldehyde, glyoxal, and
> glutaraldehyde.

I routinely handle 25% glutaraldehyde and formaldehyde as a part of my
academic career. Indeed I had to deal with it today. This is a
process to prepare specimen for microscope examination, very analogous
to embalming. I do it routinely so I know how to minimize exposure and
manage the irritating vapor. Those stocks are refrigerated, which
helps to minimize vapor. The stocks are diluted to 4% in fume hood for
use. And 200+ml of the 4% solution is used per "sample." This is
mildly irritating if I don't follow the safety limit of the fume hood
(fume hood is safe only if the opening is limited to certain area).
Both form and glut are pungent and irritating nearly equally at this
level of exposure. I do this only a couple of times a week but lab
techs are doing this all day long. This is the kind of situation for
which all sorts of warnings are written about. Employers should know
the potential hazards and must provide good working environment.
Darkrooms for some special radiographic materials use hardening bath
in trays or other large working containers and similar warnings apply.

I don't even want to have 25% stock in my darkroom though it has
pretty good ventilation. Glutaraldehyde is so much more efficient
hardener that much much less of it is fully adequate. I use up to a
few ml of 2.5% solution in a small batch of emulsion. The amount used
is already 1/1000 times less than what I use in above situation.

Another advantage of glutaraldehyde is that once bound to gelatin,
which occurs very quickly, the glut molecule won't come free. That is,
net exposure is much less than the above case after 1/1000 is factored
in. This is different with formaldehyde. Formaldehyde-gelatin binding
is reversible and formaldehyde can later get freed. This can of course
vaporize and give off smell or irritate eyes and respiratory organs.
And this is worse because formaldehyde is often used in much larger
quantity than glutaraldehyde.

In terms of toxicity, as long as usual darkroom safety precautions are
fully observed, formaldehyde, glyoxal, gluteraldehyde are no more
toxic than other chemicals commonly used in alternative processes (as
well as toners used in silver gelatin). One important thing to pay
attnetion for is good ventilation to a level so that the strong smell
is not detected, and not to continue working if the vapor comes to the
level that irritates eyes, nose, throat, etc.

For the purpose of hardening gelatin, if dilute stock solution is kept
in a narrow mouth bottle and necessary amount is dispensed immediately
before mixing into gelatin solution, I don't see how glutaraldehyde
hardeners can be dangerous. Hardening in formaldehyde or
glutaraldehyde bath is not recommended unless you have a good fume
hood or do it outdoors (large quantity of free aldehyde, large surface
area). Same thing for hardening developers occasionally mentioned in
silver gelatin literature.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)