Gelatin hardening, was Re: was: glyoxal yellowing now: How do you know it's hard?

From: Sandy King ^lt;sanking@CLEMSON.EDU>
Date: 02/03/05-12:14:58 PM Z
Message-id: <p06020400be2817555fef@[130.127.230.212]>

And of course, if it is hardened enough for your
application it may be too hardened for mine!

I don't understand the requirements of gelatin
hardening for your application, which I presume
to be gum printing, or gum over palladium, but I
do understand them fairly well for carbon
printing, in which images are transferred in
various way from one surface to another. In
single transfer, for example, where the image is
developed directly on a piece of gelatin sized
paper, the gelatin must be quite hard for the
process to be successful. For example, if one
were to fix out a photographic paper in a fixer
with no hardener, there is a good possibility
that the image will frill off the paper during
hot water development. So for this application I
fix the paper in a hardening fixer.

On the other hand, success of the double transfer
carbon process depends on having a final paper
with a relatively soft gelatin layer that will
expand a lot on soaking in water, and thus be
able to make full contact in both the shadows and
highlights with a dimensional image on a plastic
carrier. If the gelatin is unable to swell
sufficiently the highlights will be unable to
come into contact with the gelatin of the paper
support. So for double transfer I fix in a
non-hardening fixer. When I size my own art
papers for double transfer carbon I use potassium
alum, which leaves a very soft gelatin layer that
will swell a lot when placed in water at about
70 F.

This is only two or many other situations in
carbon where one must be very aware of the degree
of hardening of a gelatin size and of its
consequence on success in any given transfer
operation.

Sandy

>The whole gelatin hardening debate makes me wonder if there is any real easy
>way to tell if it(the gelatin) is hardened enough. Is it an on/off thing,
>where it is either hardened or not, or are there degrees of hardness? My
>question is asked because the amount of hardening agent should ideally be
>just the minimum needed to cause the gelatin to harden enough to keep
>highlights nice and clean.
>
>On another note, can someone point me toward a source for glut? I seem to
>recall this being mentioned on the list about 6 or so months ago, but I
>can't find it, and I'm feeling lazy.
>
>Thanks,
>
>Clay
Received on Thu Feb 3 12:15:52 2005

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