Judy Seigel (jseigel@panix.com)
Sat, 27 Nov 1999 02:00:09 -0500 (EST)
On Fri, 26 Nov 1999, Jeffrey D. Mathias wrote:
>
> But on the point of removing material, I thought that the exposed
> portions were those hardened, while those not exposed were subsequently
> removed. In the case on regular Gum this would be the underlying
> material, unless the Gum was transferred, in which case the unexposed
> (unhardened) portions would then be on the surface. Is not Gum more
> resilient to "flaking" than gelatin, facilitating a good print without a
> transfer?
The theory is that the gum layer is thin enough so there's enough
hardening down to the paper for at least some of the hardened emulsion to
hook into the paper texture or fiber -- which is why it's much easier to
keep your highlights if you print on rough paper. However, the rough
texture in the print that's printed on rough paper can in some ways
cancel that out. (The gum gods give and the gum gods take away.)
That's also why a *thick* coat of gum emulsion tends to flake.
I've read from someone somewhere (Mike Someone-Ware?) speculation that the
gum layer is much more unitary in its hardening, that the highlights are
simply *less* hardened and soak away first.
> With gelatin I had thought that it was difficult
to remove the unexposed
> portions without a transfer because of a great amount of "flaking" of
> the exposed layer that would occur.
Generally speaking it seems that gelatin coats (as for carbon printing)
are thicker, and again gelatin behaves generally differently... I think
that once it's set, gelatin is not as soluble in unheated water. If you
put a gum drop in water and a blob of jello in water,the gum drop would
dissolve first, the jello maybe not until you heat it. (I would imagine
that the "direct carbon processes" which pop up now and again (and
lately!) use a thinner coat too.)
Judy
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| World Journal of Post-Factory Photography > "HOW-TO and WHY"
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