Re: Glutaraldehyde: a different kind of cautionary tale

"One thing I've learned in reading these forums is that
glutaraldehyde-tanned leathers don't age well; within 6 to 12 months the
leather turns yellow, and soon after turning yellow it loses its
strength and integrity and can be torn as easily as paper. For this reason,
glutaraldehyde isn't recommended for the primary tanning process for
leather. It is sometimes used to add perspiration resistance to leather
intended to be worn next to the skin, like cushioning for prosthetic devices
for example, but in these cases it is recommended that the glutaraldehyde be
used as a post-treatment for leather that has
first been tanned with chrome or some other tanning agent and thus
rendered safe against the weakening effect that glutaraldehyde has when
used to tan raw (pickled) collagen."

That's very interesting. This seems to confirm what is stated in a paper
dealing with dichromated gelatin: there is a fundamental difference between
chrome hardening and aldehyde hardening. "When the commonest organic
hardener (formaldehyde) is used, the gelatin molecules bind to their amino
groups at relatively high pH values and the carboxylic groups are considered
absolutely free."(Mazakova et al, Dichromated gelatin for volume holographic
recording with high sensitivity. Part II, Optical and Quantum Electronic 14,
1982, p.318)
"The results from the experiments show that if for bias hardening of
dichromated layers a hardening agent is used which binds not the carboxylic
but, say, the amino groups of the gelatin molecules, the light energy is
used more thoroughly, i.e. the sensitivity improves." ( p.319)
I ignore how this relates to gum crosslinking though.

Martin

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, April 28, 2004 12:49 PM
Subject: Re: Glutaraldehyde: a different kind of cautionary tale

> Hi folks,
> In the process of writing my web page on the chemistry of the gum
> process, I've gotten into the chemistry of the leather tanning
> industry. In the process of exploring this sidetrack, I've discovered
> and perused the archives of two online discussion forums devoted
> entirely to the chemistry of leather tanning, sponsored by industry
> groups.
>
> One thing I've learned in reading these forums is that
> glutaraldehyde-tanned leathers don't age well; within 6 to 12 months the
> leather turns yellow, and soon after turning yellow it loses its
> strength and integrity and can be torn as easily as paper. For this
> reason, glutaraldehyde isn't recommended for the primary tanning process
> for leather. It is sometimes used to add perspiration resistance to
> leather intended to be worn next to the skin, like cushioning for
> prosthetic devices for example, but in these cases it is recommended
> that the glutaraldehyde be used as a post-treatment for leather that has
> first been tanned with chrome or some other tanning agent and thus
> rendered safe against the weakening effect that glutaraldehyde has when
> used to tan raw (pickled) collagen.
>
> I don't have any idea whether this information has any relevance to
> gelatin hardening for alt-photo purposes. I'm arguing in my website
> essay that the chrome-tanning model may not be a useful model for
> photography involving dichromated colloids, but that's a different
> issue. The fact that Ryujii uses glutaraldehyde in his work to harden
> gelatin with apparently no such result suggests that it may not be
> relevant; there may be something different about how glutaraldehyde
> works on collagen vs how it works on gelatin, or more likely IMO
> something in the tanning process itself (perhaps something in the
> pickling liquors; the tanning process is incredibly complex and uses a
> witch's brew of different liquors and salts and whatnot) that creates
> this effect. At any rate, I found it interesting in the context of
> discussions here about whether glutaraldehyde should be adopted as the
> chemical of choice for hardening gelating sizing, and thought I'd throw
> it in for whatever it's worth, which may be nothing at all. At ease,
>
>
> Katharine Thayer
Received on Thu Apr 29 01:42:11 2004