Pt/Pd printing with various lights

[Sandy King <sanking@clemson.edu>]

Title: 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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