Re: Gum woes

From: Joe Smigiel ^lt;[email protected]>
Date: 05/09/05-09:20:24 PM Z
Message-id: <s27ff048.014@gwgate.kvcc.edu>

>>> cactuscowboy@bresnan.net 05/09/05 10:18 PM >>>
"...Here's a quick and brief summary of how ratios effect the final
result.

More pigment: greater color saturation, more tendency to stain.
Less pigment: subtle color, weaker effect, better for multiple printing.
More gum, less sensitizer: prone to flaking, slower printing speed,
contrasty.
Less gum, more sensitizer: faster printing speed, less contrast..."
Dave Rose

Dave,

I've never observed that more pigment led to more of a tendency to
stain. A staining pigment will stain deeper if more concentrated but
more of a nonstaining pigment only leads to a tendency for the emulsion
to flake due ultimately to underexpose, IME. Likewise, more gum may
require more exposure or flaking could result as you mention.

Pigment stain IME is the result of having the emulsion too dilute,
either with too much water or too much sensitizer solution, or not
enough sizing, all of which allow the emulsion to soak into the paper.

Fog OTOH, is caused by overexposure and IME is more likely when using
the ammonium salt and fluorescent tubes for exposure. I have never
experienced a fogged gum emulsion since changing to a quartz halogen or
metal halide lamp and potassium dichromate, other things being equal.
(I've also never experienced "dichromate stain", only pigment stain and
fog from exposure.)

Joe
Received on Mon May 9 21:16:59 2005

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