Re: Gelatin-polymer blend (was Re: Gesso sizing)

Ryuji,

The gesso acrylic may not work for your purposes as a hardener for silver
processes but it certainly makes a hard and durable sizing for gum. I have
used it a few times and was able to coat and develop with my usual rough
brushing and even with many layers (many soakings and brushings) it held up
and the paper had not stain. I suspect the gelatin is not "hardened" but
just trapped within a matrix of acrylic.

Jack

> From: Ryuji Suzuki <rs@silvergrain.org>
> Reply-To: alt-photo-process-l@sask.usask.ca
> Date: Thu, 19 Jan 2006 17:25:42 -0500 (EST)
> To: alt-photo-process-l@sask.usask.ca
> Subject: Gelatin-polymer blend (was Re: Gesso sizing)
>
> From: Katharine Thayer <kthayer@pacifier.com>
> Subject: Re: Gesso sizing (Katharine)
> Date: Thu, 19 Jan 2006 11:53:56 -0800
>
>> I use about 30-40 ml gesso in 150-200 ml 3.5% gelatin.
>
> What's the polymer content of your acrylic gesso?
>
>>> Does this mixture need hardening?
>
> Whether it needs hardening is a different question, but blending this
> type of polymer is not a substitution for hardening. In slightly
> acidic cold water condition, the swelling of gelatin-acrylate blend is
> lower than with plain gelatin, and this itself may help the sizing
> layer to hold up, but I wouldn't rely on it at all, at least for
> silver gelatin process (emulsion is coated at 35-40C).
>
> I've tried gesso mix but one objection I had was that the acrylic
> gesso is gritty because of matting agents in the mix. Another
> objection I found is that the gesso contained titanium white and other
> things I would not want to have in my prints unless archivality is
> proven in the particular combination. Titanium white is very
> photoactive and generates a lot of radical chain reaction in the
> material when exposed to UV, and this was the main cause of problems
> in early days of RC papers. Photographic industry learned enough and
> today's products have good amount of means to prevent the problem, but
> I am not sure of gesso in sizing layer.
>
> Modern photographic films blend gelatin with hydrophobic polymer
> containing carboxyl groups, like poly(methyl
> methacrylate-co-methacrylate) in poly(acrylic acid). According to Naoi
> of Fuji Photo Film, this helps in both rapid diffusion of chemicals in
> development process, and fast drying of the material after washing. In
> terms of chemistry, apparent molecular size of the polymer blend
> changes depending on the pH of the environment (the apparent molecular
> size observed by GPC is much larger than the starting molecules). Naoi
> explains this in terms of polyion complex formation between primary
> amino group of gelatin and carboxyl group of polymer. (That is,
> isoelectric point and swelling properties of binder blend found in
> today's film and paper are not like what you find in old literature.)
>
> The blender I use is Roam and Haas Rhoplex (US) or Primal (elsewhere)
> AC-35, in the quantity of 0.5 ml per each gram of gelatin. You can buy
> this product in small quantity (cheap) from Kramer Pigmente. It has no
> questionable pigment or gritty matting agent, and blends very well
> with gelatin. Among polymer blends I tried, this was one of the bests
> and is readily available in all sorts of quantity. Then I harden the
> mixture with the bisepoxide hardener at pH 6.
>
>
Received on Fri Jan 20 08:33:49 2006