Re: Hardening gelatin

I've been hardening silver emulsion (with formaldehyde) to apply it to glass
plates - I know it's been hardened because now it doesn't fall off the
plates :). Also I note that when I harden emulsion for use on paper - this
is with "Liquid Light" btw, it is much less fragile and has far better
resistance to accidental damage. When using hardener for gelatine sizing for
gum, I don't need to recoat between layers nearly as much, as I did when
using unhardened gum. I found that if I didn't recoat between layers before,
I would always end up with staining sooner or later.

Kate
----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, March 18, 2004 11:16 PM
Subject: Re: Hardening gelatin

> While thinking about my experiment in hardening gum, I got to wondering
> how people who harden gelatin for sizing actually know that hardening
> has taken place.
>
> What I'm hardening is watercolor paint with gum added to it, the same
> gum/pigment mix that I use for gum printing. Dried unhardened gum is
> very soluble in water; that's one of the basic principles that underly
> the gum process, after all, and the added color makes it very easy to
> tell whether the gum has been hardened: just drop a drop of water onto
> the dried gum/paint and blot. If I get a round white spot where the drop
> of water dissolved the gum back to white paper, I can be sure that
> hardening didn't take place.
>
> But when you're hardening gelatin, how do you know? Since, like Judy,
> I've long questioned the wisdom of assuming that the chemistry of gum
> and the chemistry of gelatin are interchangeable, it occurred to me that
> this might be one place where I could compare the two in some kind of
> quasi-systematic way, since I have these hardening agents that are
> usually used for gelatin, that I'm using to harden gum with. If gelatin
> and gum behave similarly in this case, then I would have to consider
> softening my resistance to the idea that gum chemistry = gelatin
> chemistry.
>
> But right away I'm up against this question: if I do this comparison,
> how will I know that the gelatin is hardened? In my experience dried
> gelatin isn't as hypersoluble in water as gum is; I doubt that dropping
> a drop of cold water onto unhardened dried gelatin would dissolve it
> instantly in the same way that a drop of water dissolves unhardened
> dried gum; it would have to be hot water for that to happen, yes? If the
> hardening can't even be judged under the same conditions, how could it
> be argued that the two things are functionally the same?
> kt
>
>
Received on Thu Mar 18 15:20:58 2004