Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Thu, 20 May 1999 23:37:30 -0400
FURTHER RESULTS
For this comparison the following parameters were set:
Paper was Crane's Parchment Business Card Stock (Lot No. 5302) (or
called "platinotype")
ambient temperature at 68-72F
AMBIENT RELATIVE HUMIDITY at 60 %, 70 %, and 85 %
chemistry for 8x10 was 24 drops sensitizer, 1 drop contrast agent, 24
drops metal salt
coating by brush
drying with ambient temperature blow dryer
exposure was 4.5 minutes under my artificial lamps
processing was identical to previous runs
Please note that while I can regulate and maintain the ambient relative
humidity to a relative accuracy slightly better than +-1% in my
darkroom, my humidity meter reads with an absolute accuracy of +-5%.
Best control is achieved with the simultaneous use of dehumidifier and
mister.
Prints were compared by looking at dry in "normal" light and direct
sunlight (reflected and transmitted). The overall evaluation was to
judge the quality of the print with emphasis on darker areas. I used
the same image of a dark stairway with lots of shadow details and
texture. I also included a "21 step" in the print. It must be
understood that the evaluation might be influenced with another image
and normal printing variations.
Various concentrations of the Li2PdCl4 were used, but all had the LiCl
and PdCl2 balanced.
I also again checked two concentrations of the Ammonium Ferric Oxalate,
40 % and 60 %.
I found that the proper drying of the coating was again an important
step. The coatings were dried with low forced air at ambient
temperature. Every coating was felt with the back of my finger and was
considered dry when the coating just did not feel sticky, just dry to
the touch (paper was limp with no crinkle). This time the 8x10 negative
would not curl when placed on top of the coating, already being at
ambient humidity. After two prints at 85%RH the negative felt like it
had some residue sticking to it although nothing was visible. After
making seven prints, I washed the negative. At the 70%RH and 60%RH
there was no sticking and no residue left on the negative.
The coatings at 85%RH were very tedious to dry. The prints showed
graininess (some severe) which could likely be attributed to improper
drying of the coating. It seems that it will be an overwhelming
challenge to properly dry coatings at ambient relative humidity above
80%. None of the coats at 70%RH and 60%RH seem to have any problems
with graininess. However all of the prints had a nonuniform color,
patches of warm color (more on this later). Evaluations were made on
the more neutral color portions.
The sensitizer was used at 24 drops of 40% (for all concentrations of
metal salt) and 60% (for 30.62% and 24.49% concentrations).
All prints used a contrast agent of one drop 0.5% Ammonium Dichromate.
The metal salt was used at the following concentrations (same as last
time; # drops indicates concentration equivalent to drop method used
before):
drops Li2PdCl4 solution Drops H2O % concentration Li2PdCl4
20 4 30.62
16 8 24.49
12 12 18.37
8 16 12.25
As previously reported, no difference was noted between the sensitizer
solutions of 40% and 60%.
At 85%RH, there seemed to be little difference between prints except
that the higher concentrations of metal were much grainier. All prints
were grainy looking and weak.
At 70%RH, only the 8 drop concentration seemed slightly weaker.
At 60%RH, the 8 drop print was definitely weaker and the other
concentrations looked identical.
The speed of all prints seemed identical.
The contrast of prints went down as the ambient RH went up. The change
seemed to be around ½ grade overall.
But,
WHAT A MESS.
Most prints had blotchy color, some neutral and some warm. Whether
coincidence or not, the neutral color was mainly confined to one end of
the print and the warm color was mainly confined to the opposite end.
This occurred in most every print and when it did occur, it seemed to
follow the same pattern. I attempted to find if the pattern was a
result of lights, printing frame, or processing. I could not find any
relationship; however I could makes prints without the problem.
A NEW REVELATION:
At the 60% ambient RH, I decided to try to fix the color mess.
First I tried a coating of:
Sensitizer at 24 drops of 40%
Contrast agent of one drop 0.5% Ammonium Dichromate
21 drops Li2PdCl4 at a concentration of 24.49% plus 3 drops K2PtCl4 at
20%
This resulted in a much more neutral color and better detail and
substance in dark areas. However the warm blotches of color, although
greatly reduced, were still present. It also seemed that a nice split
tone might come of this (further work is needed).
Next I tried a coating of:
Sensitizer at 24 drops of 40%
Contrast agent of one drop 0.75% Potassium Chlorate
24 drops Li2PdCl4 at a concentration of 24.49 %
This resulted in the most neutral color AND no warm color blotches.
WOW! It seems that the Ammonium Dichromate may be an undesirable
ingredient of the coating. Past experience has shown me that more
Potassium Chlorate is needed to produce the same contrast as Potassium
Dichromate so I assumed it might be the same for Ammonium Dichromate.
The 1.5 times seemed close, but a more accurate comparison should be
done.
I plan to check on the optimization without using Ammonium Dichromate.
SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS (including previous results):
+ Li2PdCl4 should be mixed with the proper balance of LiCl and PdCl2.
+ Concentration of Ammonium Ferric Oxalate works fine at 40%.
+ Ambient relative humidity should be kept above 50% (especially for
testing).
+ Ambient relative humidity should be kept below 80%.
+ Special care must be given to proper humidification of the coating at
less than 50%RH (ambient).
+ Proper drying of the coating at more than 80%RH (ambient) is
extremely difficult and most likely not capable.
+ Special care must be given to protection of the negative only at more
than 80%RH (ambient).
+ Optimum concentration of Li2PdCl4 was determined to be 24.49%, but
may be reduced at higher ambient relative humidity.
+ Addition of some platinum salt produces more detail and a more neutral
color and perhaps a split tone.
+ Ammonium Dichromate should not be added to the coating. <<<<<<<
+ Potassium Chlorate can be used as a contrast agent and will result in
a very neutral color.
Disclaimer: As is the nature of the Pt/Pd process, results will vary so
comparisons should be made carefully.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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