Re: glutaraldehyde

On Thu, 18 Mar 2004, T. E. Andersen wrote:

> This may well be the case, but the mechanical durability of the very
> hardened films comes at a cost. If you want very hardened gelatin, you
> can get that even with formaldehyde, since even this cross-links to some
> extent (due to short-chain polymers, if I remember correctly).

To interject a note of practical observation into this barrage of
theory... I've found many times, especially in gum printing, that the
*theory* is theoretical and does NOT work that way in the event. I've
seen this almost to the point of comedy when folks extrapolate about
"findings" cited in Kosar re dichromates tested in carbon and apply them
to gum printing. It doesn't work that way.. I think it would be better to
rationalize the gum *findings* by dialing up the theory after the fact.

Equally important, I'm skeptical of *absolutes* about either
glutaraldehyde OR formaldehyde OR for that matter glyoxal and their effect
on gelatin on paper IN THE ABSTRACT -- that is, without citing specifics
of the handling. For instance my tests, really dumb, like chair caning, I
didn't know diddle about cross links or short-chains, but I tested the
same gelatin on the same paper with several different strengths and
lengths of hardener -- and found the results of weak v. strong, and long
v. short hardening as they affected staining (which is the object of
sizing) to be QUITE QUITE QUITE different.

I don't know any other way to test the effects of a hardener, tho maybe
there's a photomicrograph that shows crosslinks -- and if so, what does
that tell you -- it does NOT tell how it behaves with this or that on top
of it, soaked, scrubbed or boiled.

My tests also show, by the way, that when your size is TOO hard, you lose
highlights because the gum layer tends to roll off. So the "right"
treatment CANNOT be decided by a book or theory, ESPECIALLY one geared to
silver gelatin emulsion.

Meanwhile, Tom, there are prints that were hardened in formaldehyde that
still look pristine after 100 years... But a suggestion: 15cc of 40%
glyoxal in a liter of water did the best job, cleared best, tho the books
will tell you 25 cc. And beside all the other reasons for not putting the
hardener in the gelatin, I point out that then you can only use it one
time. When you've mixed a gallon of the stuff to get big prints covered,
it's nice to be able to keep it for a few days.

good luck,

Judy

>
> My primary reason for wanting to do alt-photo in the first place, is the
> ability to produce prints with very high life expectancy. This is not
> the first consern for commercial print papers or photographic films.
> Rather they need to accomodate the demands of high-speed presses and
> developing machines. Most of what these machines produce is designed to
> last only for a short time.
>
> >
> >> On the other hand, it may well prove to reduce the archival
> >> properties of the coating. I do not know this to be the case, but I
> >> would not be surpriced if it did. After all, the more cross-linked
> >> the proteins are, the more brittle the gelatin will be, and the
> >> less of the protein molecules will be free to adhere to the paper
> >> and image layers. Again, I do not know this to be a problem, but
> >> it's fair assumption.
> >
> >
> > I suggest you study literature before making such a speculative
> > comment. Hardening of gelatin have little influence on mechanical
> > properties of dry gelatin. Also note that gelatin is degraded
> > collagen product and is a bit different from proteins you are
> > accustomed to.
>
> You may again be right, of course, but I don't see how gelatin can be
> *that* different from other proteins? I have not read the literature
> from the photo industry on this, but I *have* read quite a few volumes
> and articles from tissue research. Are you suggesting that the basic
> mechanisms of fixation are somehow different in gelatin? If so, why is
> that the case?
>
>
> >
> >> I have not used glyoxal (HOCCOH) yet (but I've bought a bottle to
> >> test). It's similar to glutar aldehyde (HOC(CH2)3COH) in being a
> >> dialdehyde, so it too, is cross-linking.
> >
> >
> > Glutaraldehyde is superior cross linking agent to glyoxal and
> > formaldehyde because GTA is bifunctional, meaning that it can attach
> > to two separate gelatin molecules. I suggest you study literature
> > before making speculative comments here, again.
>
> Why do you consider the glyoxal monofunctional? It, too has two aldehyde
> groups. Does only one react with proteins?
> (As far as I know glyoxal is not used in microscopy, and I have no
> scientific knowledge of this compound, other than what I have read in
> the Merck Index. If you have references dealing with the reactions of
> glyoxal with proteins, I'd very much like to get a short list if possible.)
>
>
> Regards,
>
> Tom Einar Andersen
>
>
> Ps. I saw the ref. list you sent in another posting. That paper dealing
> with the effect of aldehydes on bread and croissants really makes me
> want to bake my own bread.... Why on earth would anyone want to use
> aldehydes on bread????
>
Received on Wed Mar 17 21:34:29 2004