From: Sandy King (sanking@clemson.edu)
Date: 04/10/02-01:49:44 PM Z
Katharine Thayer wrote:
>
>I don't know if Sandy was responding to anything in my post or in this
>thread by his statement above ("image stain with well-exposed negatives
>does not appreciably increase printing time") but in case he was, I
>don't think that it's a question of printing time, but of how well the
>negative blocks the wavelengths responded to by the sensitizer in
>question.
>kt
Yes, my original point was that stain is a filter to actinic light
and as such can cause an increase in printing time. I take that to
address your question above, i.e. how well the negative blocks the
wavelengths responded to by the sensitizer in question. It stands to
reason that printing time will increase with an increasing efficiency
of the negative to block the wavelengths responded to by the
sensitizer.
Is that wavelength different for gum and platinum? Lots of published
data and anecdotal reports suggest that the iron sensitizers of
kallitype and platinum have a lot of sensitivity in the 400-500 nm
range, while the sensitivity of dichromated colloids drops off to
almost nothing after about 420. Therefore, if a negative filters out
all of the wavelength between 400-500 nm this should have more of an
impact in platinum printing than in gum.
Sandy King
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