re.gum bichromate

Roy Brown (RB10024@hermes.cam.ac.uk)
Tue, 27 Jun 1995 16:37:03 +0000

On the subject of thickness of coating, I too have had flaking, which I put
down to a too thick layer. Same emulsion, thinner coat, same exposure has
then worked. Presumably if the coating is too thick, the emulsion nearer to
the paper may not get exposed, and so remains soluble. Add water and hey
presto it dissolves, taking with it anything above, whether hard or not.

I would imagine tri colour gums are a nightmare because after the first
coating, the paper has in effect had another coat of size. Stronger /
weaker size also affects the adhesion of the emulsion, so does each coating
need different gum/pigment ratios?
Why do we do this?

Roy.
P.S. I've only been into gumbi for about 18 mths, so this is not gospel!

Roy Brown | e-mail rb10024@hermes.cam.ac.uk
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