FotoDave@aol.com
Date: 11/12/01-08:19:19 AM Z
<< Like we used to say in the olden days: you said a mouthful-- about
applying "standard" sensitometric tests... especially since each color
exposes differently even before you consider emulsion thickness. >>
Hi Judy,
Actually I didn't say much about applying "standard" sensitometric tests. I
said about the difficulty of applying such tests. Of course each color
exposes differently, but that wasn't under discussion. Assuming the same
color, in fact, I mentioned that for *same* emulsion mix, same paper, same
sizing, etc. thickness could affect speed.
My message was mainly in response to Sandy's message with a statement in the
multiple-choice questions about gum printers by nature is incapable of
applying sensitometric tests (which I took as half joking and didn't take it
as offensive), and so I responded by saying that it might not be the
problem/fault of the printers but the process itself, and I illustrated with
one example only concerning thickness.
<< But what photomechanical laws are we talking about? Do I know them?
>>
I didn't mean to pinpoint certain specific laws but in general sense the laws
of exposure, hardening, etc. Gum printing certainly obeys certain laws,
otherwise we wouldn't be able to make any print at all, would we? Some of the
laws we more or less know, like if the emulsion is applied super thick, the
image will wash out. The law of exposiure and gum hardening is probably be
the same as in a thin emulsion, but the hardened layer is not deep enough to
hold on to the paper base; or if different colors are used, the exposure will
be different. There are other laws that we might not be able to explain that
easily probably because we don't have all the information, like if we switch
brand of watercolor, things would change.
But I admit that I went off the original topic. I wasn't staying with the
original discussion of the change of dichromate in a bottle.... my whole
message was simply a "gentle defense" that it is not the gum printers who are
incapable of applying standard sensitometric tests but rather the process
itself makes it difficult. :-)
Dave S
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