gelatin hardening (was Re: Glutaraldehyde: a different kind of cautionary tale)

From: MARTINM <martinm@SoftHome.net>
Subject: Re: Glutaraldehyde: a different kind of cautionary tale
Date: Thu, 06 May 2004 14:24:29 +0200

> Moreover there is heat treatment (which may not simply cover baking
> but also micro-wave exposure) to provoke strong crosslinking. Heated
> gelatin is said to form in situ aldehydes.

Are these techniques used for any photographic products? I don't
think so. For one thing heating of gelatin affects too many factors
and using chemical agent is more controllable way to accomplish
hardening. Aldehydes are a known microconstituent of gelatin products,
although photographic gelatin is produced so that it is free of
aldehydes.

> Though producing similar effects as more conventional hardeners, I
> am not sure whether introducing monomers into a gelatin layer that
> are subsequently polymerized, may be regarded as hardening.

What is being polymerized?

> It seems to me hardening involves the melting point of gelatin to be
> risen. However, this appears to be somewhat ambivalent since
> gelatin concentration is likely to have a large impact on gel
> strength.

> One criterion might be to what degree/at which temperature gelatin is
> swelling - that's to say, the quantity of water bound within the layer.

Hardening is a way to influence the mechanical properties of gelatin
in gel state. This is most commonly measured as amount of swelling of
gel at a certain standard condition. Melting point also changes, but
it is less readily measurable quantity.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)