From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 12/28/00-09:20:06 AM Z
Sarah Van Keuren wrote:
> I agree with Judy's distinction between a printing-out-process and a
> printing-out-paper. A distinction I make that Judy may not make is between
> an emulsion and a chemical solution. P.O.P. with silver chloride salts in a
> gelatin coating is for me an emulsion. Gum bichromate with pigment suspended
> in sensitized gum arabic is also an emulsion. The trick with syrupy
> emulsions is to attach them to the support but to keep them on the surface
> of it. Cyanotype, vandyke, palladium, platinum and ziatype are all chemical
> solutions, watery mixes that soak into the fiber of the paper. I think it
> helps those who are learning alternative processes to understand this
> distinction. Does anyone else find this a helpful distinction?
I also feel the distinction of an emulsion attached to the surface of a
substrate and a coating solution imbedded in the surface of a substrate
is important and relevant to the understanding and mastering of various
processes.
It is important to understand that Pt/Pd coatings (and some others) are
not an emulsion. Some examples: Even a thick coating that does not
penetrate the substrate can just wash off during clearing. The surface
of the final print is not covered with another material (even though it
could be). The substrate or additives within it may react with the
coating chemistry or provide for effects in the image. Non-uniform
depth of penetration, such as soak through, can cause effects in the
image.
This is not to say that there are not many considerations when working
with emulsions, just that there can be many differences between
emulsions and solution coatings which can impact process, technique, and
method.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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