On Fri, 12 Mar 2004, pete wrote:
> ... The British have been using gloy gum for a number of years to good
> effect. Gloy is a PVA emulsion and is more viscous than gum and allows
> for mechanical abrasive washing of procedures. Whereas the traditional
> gum is far to tender and only natural development will do. The
> childrenšs PVA is even more viscous than gloy and will withstand a heavy
> loading of pigment before losing its adhesion.
Sorry, this is quite wrong... "PVA is more viscous than gum" is an
unanchored absolute. There are many PVAs and many gums, besides which
"viscosity" is changed once the dichromate and color are added, and in any
event, the image is created not by viscosity but by the dichromate
hardening the colloid.
For example, casein as colloid is often quite watery, seems not to have
any *viscosity* at all... yet its developing image almost DEMANDS spray,
brushing, or other abrasion. You CANNOT connect ability to abrade with raw
viscosity of the colloid. (I'm also not sure what you mean by viscosity
anyway... thickness? If so, you can mix a thicker gum.... tho I wouldn't.
I like a thinner gum.)
As for the idea that "traditional gum" can only do "natural development"
-- wrong again... Aside from the time-honored gum manipulations of
dripping, pouring, spraying & sponging water, & brushing, et al., I have
often developed a gum print with sawdust. Yes, a sawdust slurry. No big
deal if you understand the operation -- expose harder and soak shorter.
And/or use a higher ratio of dichromate to make a harder image.
Judy
Received on Fri Mar 12 20:13:41 2004
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