From: Judy Seigel (jseigel@panix.com)
Date: 10/17/01-05:32:53 PM Z
On Wed, 17 Oct 2001, Sandy King wrote:
> I am not an expert on gum printing but work extensively with carbon,
> a dichromate colloid process that has similar spectral sensitivity
> requirements to gum, per the research outlined in Kosar's Light
> Sensitive Systems. Kosar's conclusions, which I have observed in
> practice in carbon printing, is that dichromate colloid systems have
> their greatest sensitivity, but lowest contrast, in the wavelengths
> of 350 nm and below, and decrease in sensitivity but increase in
> contrast as the wavelength increases.
Sandy, I've read Kosar, for gum found it perfectly useless. I daresay
Katharine will correct me if I'm wrong, but from MEMORY, it was Kosar who
said the dichromates have a straight line, which they do in gum on
alternate Mondays when your mix has angel dew. I don't recall if he
included gum specifically, but he didn't exclude it -- which is to say I
wouldn't take whatever in Kosar on faith (yeah, I repeat myself) unless
I've tested it myself, and maybe not even then.
I think, suspect, assume, the "point of greatest sensitivity" is not the
(entire) issue, because there are in fact SPIKES at other wavelengths that
are higher, the different media and different colors have their own
sensitivities, etc., etc. In other words, these generalisations are not
definitive, may send us down dead ends, or cause us to overlook something
better.
> Speed of the printing source, within a certain range of wavelength
> (say 300-450 nm) appears to be more dependent on wattage than the
> exact wavelength of the light source, or so my tests show.
Oh yum, yum... Did you put those tests on the list?
best,
Judy
This archive was generated by hypermail 2b30 : 11/02/01-08:55:27 AM Z CST