From: Giovanni Di Mase <gdimase@hotmail.com>
Subject: Re: polivinyl alcohol vs. gelatin sizing
Date: Sun, 31 Jul 2005 07:16:40 -0400
> You said that the PVA needs to be mixed with gelatin (gum?) for the
> sizing, Kevin said that it does a perfect and complete sizing by
> itself (no gelatin, no preservative, no hardener).
I didn't say that. I said poly(vinyl acetate-co-alcohol) is best
utilized as a gelatin blend. But I do think gelatin works better than
any of those used as the sole sizing material.
PVA may work but I don't think it is a superior option to
gelatin. Ideal sizing material has good adhesion to substrate and to
the subsequent coating layer. It also has swelling property
intermediate of the substrate and the subsequent coating
layer. Material like acrylic medium (without further blending with
gelatin) has poor adhesion to the subsequent coating layer, and they
don't swell enough. Polymers that dissolve without swelling, or
polymers that don't swell at all are inferior. Of course, polymers
with poor adhesion are inferior. Gelatin can swell without
dissolving, while maintaining good adhesion and these properties can
be modified by incorporation of addenda like hardener and other
polymers. Gelatin is a very useful material for sizing as well as
binder in some processes.
In water solution, poly(vinyl alcohol) is clear, poly(vinyl acetate)
is white, their copolymer is also white.
Acrylic medium contains poly(alkyl methacrylate) as the acrylic
material, of course. Usually, poly(methyl methacrylate) and poly(ethyl
methacrylate) granules (of very fine particles) are used. These are
the ingredients that give very strong surface durability and somewhat
matte look when the acrylic medium dries. In commercial silver gelatin
material this type of material seems to be blended in the overcoat
layer to reduce friction and also to give various matte look. I would
not use acrylic medium as the sole sizing agent or the sole binder for
the same reason I said above.
Received on Fri Aug 5 12:01:28 2005
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