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Sandy, As platinum and palladium have
different response curves, you have been only able to test an undetermined
coating with three different light sources. I would not make any
conclusions about all platinum/palladium coating based on these test.
Since platinum and palladium are both speed sensitive with regard to humidity,
they indeed have been shown to react to differing wave lengths to produce
different yields, I find your test to be too loose to "prove" anything beyond
that all three react to your lights with equal +/- results.
EJ Neilsen
----- Original Message -----
Sent: Wednesday, May 08, 2002 8:14
PM
Subject: Re: Pt/Pd printing with various
lights
Eric,
I agree that if the purpose of my test had been to compare the absolute
speed of different processes it would have been best to coat, dry, expose and
develop all of the samples in my environment. However, the purpose of
these tests was not to determine the absolute printing speed of the Pt/Pd
material vis a vis another printing process, but its relative speed with
different lights. In that sense I believe that the results of the test are
very reliable. I made three different test prints with each light and results
were almost identical for all three tests made with a specific light. If any
one test had been off with respect to the other two it would be reasonable to
suspect a difference in speed or contrast in the samples and that would of
course have invalidated the test results. Since this was not the case,
however, I am reasonably certain that these results are valid.
Sandy
Sandy, I
would think that a better test would be to coat them yourself. Speed
changes in paper and contrast may change to much sitting for a day or
more.
----- Original Message -----
From: Sandy
King
To: alt-photo-process-l@sask.usask.ca
Sent: Sunday, May 05, 2002 6:53 PM
Subject: Pt/Pd printing with various lights
A few weeks ago I posted some preliminary
observations on the use of different UV sources with Pt/Pd. As you
may recall I exposed a Stouffer TP 45 step wedge to paper coated with Dick
Arentz' Pt/Pd Mixture #7, using the following light sources: 1) 20 watt
Phillips BL, 2) 20 watt GE BLB, 3) 75 watt URI Super Actinic,
and a 1000 watt HID-Mercury Vapor lamp. Today I read the densities of the
tests and plotted curves with Davis' Plotter program, with the following
results.
BL
BLB
SA* HID
Speed Point
2.5
2.4
2.3 2.2
Exposure Scale
1.31
1.36
1.23 1.31
IDMax
1.17
1.20
1.23 1.31
* I also tested the 20-watt Phillips Super Actinic tubes and
the results were virtually identical to that of the 75-watt URI
tubes.
*The HID-Mercury Vapor lamp was tested with a center filter
which reduces printing speed by about two full stops. Without the center
filter this lamp is faster than at least one full stop than any of the
other lights.
For those not familiar with the above terms, here is some
explanation of terminology.
The Speed Point indicates the speed of the material and
is expressed here in relative terms. The higher the number the faster the
printing speed. The values are in log units where each value of 0.1
represents one-third of a stop, or 0.3 corresponds to one full stop. Thus,
the BL tubes turned out in these tests to be one-third of a stop faster
than the BLB tubes, two-thirds of a stop faster than the SA tubes, and one
full stop faster than the HID-Mercury Vapor lamp (with the center
filter).
Exposure Scale is the range between the minimum and maximum
density values required to print all of the tonal values. It is also
expressed in log values, with each 0.3 units corresponding to one stop. An
ES of 1.3, for example, corresponds to 4 1/3 stops. ES relates to image
contrast, the lower the number the higher the contrast.
IDMax is the value that corresponds to 90% of maximum
black.
There have been quite a number of claims that Super Actinic
tubes are faster than BL and BLB tubes for printing in platinum. My tests
show the opposite. However, the SA tubes did produce images with more
contrast than any of the other lights.
Just for the record I ran the tests three times and the
results were very consistent. Over 95% of all readings of the three tests
made with a specific light source were identical, and no difference
greater than log 0.02 was observed.
Comments and questions about these tests are
welcome.
Sandy King
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