Re: UV Sources
John Rudiak (email@example.com)
Wed, 29 Nov 1995 17:00:05 -0700 (MST)
more on uv sources a contrast colntrol. As a commercial platinum printer
(for almost 20 years now) i have used many different light sources. At
one poiunt my studio had two units capable of exposing 16X20 in
negatives. One unit had 10 four foot unshielded black light tubes (F40BL)
and the other had 12 four foot shielded tubes (F40BLB). I used these for
about one year, and the F40BLB's are definitely not useless for our
purposes, they merely required twice the exposure times of the unshielded
tubes, and you didn't need to wear UV blocker sunglasses when printing.
BTW, my normal exposure for a good negative (fb+f of 0.1- 0.2) is three
minutes under the unshielded box, using a Pt/Pd emulsion with no contrast
If you add peroxide to cut fog, it is not contrast control.
There should be no fog to start with. My procedure starts with 0.02ml.
of 3% peroxide per ml. of sensitizer and can go up to .1 ml., with
increaes in contrast all the way and no increase in granularity. I use a
sereological pipet to measure the peroxide, and add it the the sensitizer
just prior to coating. Peroxide works with any developer, also.
While it is true that Pt and Pd have different printing speeds,
something synergistic happens when they are mixed together. I have
found no difference in exposure in sensitizer mixtures from 50/50 Pt/Pd
to 10/90 Pt/Pd, but there sure is a change in color.
more later, i hope.