Keith Schreiber (jkschreiber@worldnet.att.net)
Wed, 24 Mar 1999 04:09:22 -0700
As promised, here are the results of my latest testing of the full range (7
"grades" plus zero) of Potassium Oxalate / Sodium Dichromate developer for
Pt/Pd. This test was conducted using 100% Pd. When time permits, I will do
50/50 Pt:Pd. The paper is Cranes Parchmont. Each 5x6 inch sheet was coated
with a glass rod using 0.4 ml of a solution of equal quantities ferric
oxalate and sodium tetrachloropalladate. Exposure to a Stouffer 4x5 inch
21-step tablet was for 10 minutes to a bank of 10 Voltarc Actinic
F20T12/AQA/BP-40W tubes at a distance of 9 inches. Development temperature
70 degrees F. Clearing in 3 trays EDTA/Sodium Sulfite - one tablespoon of
each per liter of water.
The purpose of this test is to see how the effect of the dichromate may have
changed with use and over time. This set of seven 2 liter bottles of
Potassium Oxalate (KOx) - with 1, 2, 4, 8, 16, 32, and 64 drops of 50%
Sodium Dichromate per 200ml of developer - have been in use since late in
1995, replenished as necessary in increments of 200ml. As a control, I have
included a test print developed in straight KOx. The results are listed as
exposure scale (ES) as calculated by the BTZS Plotter program. The ES of a
paper (or in this case, of a developer) is equivalent to the density range
(DR) of a negative needed to produce a full scale print on that paper
(developer) with no sacrifice of highlight or shadow detail due to the DR
being beyond the ES. (This does not take into account the compression of
tones in the toe and shoulder.)
Test Date 2/11/96 3/23/99
KOx 1.84 1.92
#1 1.88 1.94
#2 1.68 1.81
#3 1.64* 1.71
#4 1.44 1.57
#5 1.37 1.45
#6 1.28 1.42*
#7 1.18 1.25
Notes:
1. In both tests, KOx #1 has a slightly longer scale than plain KOx. Go
figure ;-)
2. The consistently higher ES figures (< 0.1 in most cases) for the new test
series could be the result of
- different densitometer
- different paper (1st test used Cranes Platinotype)
3. First test series showed slight but noticeable weakening of Dmax above
#4. In the new series, there is none except for KOx #7 which is only very
slightly lower (0.05).
4. Unlike when using the traditional K chlorate method of contrast control,
there appears to be no loss of printing speed with increasing contrast.
5. Visual inspection of the test series clearly shows a loss of one step in
the highlight end of the scale for each increase in dichromate
concentration, with no change in the darkest shadows.
6. #3 in the original test series and #6 in the new series are anomalous in
spacing and should be retested.*
In conclusion, I think it is safe to say that my replenished KOx/ sodium
dichromate developers have not deteriorated in the 3-plus years that I have
been using them.
Keith Schreiber
jkschreiber@worldnet.att.net
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