From: Sandy King (sanking@hubcap.clemson.edu)
Date: 05/11/01-12:16:35 AM Z
Judy Seigel wrote:
>In the early days, ammonium was (I THINK) not common & more expensive. But
>I suspect that carbon printing is done to closer tolerances (mmmm, good
>phrase) than gum... Anyway, once you have mixed your sensitizer, even if
>it's 10 or 20% off, you're using the same stuff, so you're constant.
The way I work carbon is that I adjust the strength of the sensitizer to
the DR of the negative being printed. With a sensitizer of known strength I
can be sure, for example, that a potassium dichromate sensitzer of 1% is
good for a negative with a DR of about 1.1, whereas a 6% solution works
with DR of about 1.6. With sodium dichromate I might measure out 10g of the
chemical to mix with 1000ml of water for a 1% solution, but if the
dichromate had previously absorbed a lot of moisture from the atmophere the
actual equivalent might be only a 1/2% solution, or perhaps even less.
This would dramatically change the printing qualities of the negative. You
don't have this kind of problem with ammonium and potassium dichromate.
I believe the same kind of relationship exists in gum printing but it is
not so readily apparent to you folks because you work is kind of, shall I
say, free-hand as opposed to mechanical.
Sandy King
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