Re: gum bichromate

Russell Cothren (rcothren@comp.uark.edu)
Tue, 27 Jun 1995 12:01:45 -0500 (CDT)

I was wondering??? Can a person use a plate coater like the ones
we used for coating litho plates? Its design is very basic. It consists
of two rollers about two inches in dia. They are in an over under fashion,
that is to say they sit on top of each other. The bottom roller has a
tray that it sits in and you pour your chem into the tray. The bottom
roller transfers the chem. up and onto the sheet as you pass it between
the rollers. The top roller acts as a squeege an rolls off excess chem.
The machine is elec. motor driven and the roller settings are adjustable
for proper squeeze. Our printing plates were .007" and made of aluminun.
The coatings were always nice and even. When finished you drain extra
chem. back into bottle for future use.

I have also heard of using an air brush to coat paper.any one?

RUSSELL
DONEOn Tue, 27
Jun 1995, Dan Shapiro wrote:

> I have found that gum prints flake when the coating is too thick. In
> theory, the outer layers harden without establishing a good physical
> bond to the paper fibers. Once water gets underneath the crust, the
> exposed emulsion lifts off in pieces.
>
> I have this nasty feeling that the process of coating paper with the gum
> solution is *the* most sensitive variable in gum printing, meaning that
> a small deviation from the "right" thickness causes big differences in
> print quality. Or, more to the point, coating is the easiest step to
> mess up.
>
> Do others agree? We have talked about the variables in gum printing,
> but we haven't really discussed their sensitivity. At the same time,
> sensitivity questions make all the difference when you are staring at a
> disasterous print and want to know what to do *next*.
>
> Dan Shapiro
>
>