Jeffrey D. Mathias (firstname.lastname@example.org)
Wed, 12 May 1999 11:07:13 -0400
OK, OK, I give this another try.
After hearing from Eric Neilsen I have found that I had the formula for
Ferric Ammonium Oxalate incorrect. The correct formula should be
(NH4)3Fe(C2O4)3-3H2O [Note: no twos]
Thanks to Eric for catching this.
This is closer this time but needs more work. Please do not miss the
experimental results later in this post.
The equations should go something like this?
[I have added some notes to help explain things.]
For the Ziatype variation, Ferric Ammonium Oxalate is used as the
sensitizer with a basic reaction as follows:
(NH4)3Fe(C2O4)3-3H2O =(via exposure)= Fe(C2O4)2 + (C2O4) + 3(NH4) +
[This is the oxidation reaction by which the Ferric (valence of +3) is
converted into Ferrous (valence of +2). This happens on exposure to
light. However this can also happen or be affected on exposure to heat
and time (and other things) so procedures should reflect this. The best
procedure is to coat each print immediately prior to exposure.]
I am not sure where the ammonia goes. And, I am not sure if CO2 is
created. However these should be fairly immaterial at this point.
The basic Pt/Pd process reaction with Lithium substituted should be
3[Fe(C2O4)2] + 2[Li2PdCl4] = Fe(C2O4)3 + 2FeCl3 + 2LiCl + 2Pd + 3(C2O4)
[This is the reduction reaction by which the metal is released (reduced)
from the metal salts.]
NOW, here is part of the discrepancy. How is the Cl balanced? Is FeCl3
Work is needed on this part of the equation so that it may be balanced.
The balanced equation is needed to determine the amount of ingredients
to use that will not just end up being wasted. If either the sensitizer
or the metal salts are used in excess of the ratio, that amount, in
excess, will go unused.
Looking up the molecular weights of the ingredients:
FW of (NH4)3Fe(C2O4)3-3(H2O) is 428.06
FW of Li2PdCl4 is 262.09
FW of LiCl is 42.39
FW of PdCl2 is 177.31
And here I would like to question the FW of Ferric Ammonium Oxalate as
From solid state physics book periodic table:
It follows that:
Where have I gone wrong? (If indeed I have.)
AND NOW SOME FURTHER RESULTS
For this comparison the following parameters were set:
Paper was Crane's Parchment Business Card Stock (Lot No. 5302) (or
ambient temperature at 68-72F
three ambient relative humidities at about 35 %, 50 %, and 70 %
chemistry for 8x10 was 24 drops sensitizer, 1 drop contrast agent, 24
drops metal salt
coating by brush
drying with ambient temperature blow dryer (except "full dry" which used
exposure was 4.5 minutes under my artificial lamps
processing was identical for all:
30 sec. in Potassium Oxalate (just in case and to be consistent with
2 minutes in water (all "water" was 0.5 micron filtered tap water)
8-10 minutes in each of three clearing baths
clearing agent was with Phosphoric acid (2oz. 85% reagent grade in 1
washing for 8-10 minutes in water
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 an
image of a dark stairway with lots of shadows 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 importantly, it
must be understood that under some of the conditions what could be
considered normal printing variations could be larger than the
differences observed making repetition necessary.
It was decided to not use the published formula as this had already
proved to be inferior in the previous test. I did repeat that test and
got identical results except for the color (This will be explained
later). Various concentrations of the Li2PdCl4 were used, but all had
the LiCl and PdCl2 balanced. It is agreed that an amount of LiCl equal
to twice the error of the scale used be added so that any error will not
result in a surplus of PdCl2.
I also checked two concentrations of the Ammonium Ferric Oxalate, 40 %
and 60 %. I reported on this last night. As no difference was seen,
more material was used, and surface problems with the coating could
readily happen, the recommendation was to stay with the 40%. Although
one should consider the 60% if concentrations of metal salt are used in
excess of what the balanced equations show.
I found that the drying of the coating was an important step. At 70%RH
and 50%RH the coating was dried with low forced air at ambient
temperature. At 35%RH the coating was dried with low forced air at
ambient temperature then humidified with a sonic mister (except for the
"full dry"). Every coating (except for the "full dry") 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). The 8x10 negative would curl when placed on top of the
coating. The were no instances were the negative stuck to the coating.
Prints done at the 50%RH and 70%RH were quite consistent. Prints done
at the 35%RH showed variability due to what I would consider a variation
of humidity in the coating. (Corners or spots would be warmer in
color.) On these prints, I only compared portions having the same color
as the 50%RH.
As to color, the prints at 70%RH were the most neutral. The "full dry"
print was a sepia brown with dark areas not as intense (not as dark) and
there was a decrease in speed but the same contrast, however the lack of
intensity of the dark areas was not due to speed alone. Note that
prints made with potassium or sodium with the palladium produce a much
deeper dark. The prints done at 35%RH for the most part had the same
color as prints done at 50%RH, however most had patches of warmer
color. It seems that it will be a challenge to properly humidify paper
at ambient relative humidity lower than 50%.
The sensitizer was used at 24 drops of 40% or 60%.
All prints used a contrast agent of one drop 0.5% Ammonium Dichromate.
The metal salt was made at the following concentration (number just
picked by guess):
% LiCl PdCl2 H2O
36.74 5.94 g 12.43 g 100ml
Prints were made with the following metallic salt concentrations:
drops Li2PdCl4 Drops H2O
All of these concentrations were made at 35%RH and 50%RH but only one
(as well as the published vs modified test done previously) had been
made at the 70%RH. Plans are to make these prints when I get my
darkroom back up to the 70%RH (need another sonic mister or a rainy
day). It is important to do this test at the 70%RH as it seems that any
differences become more apparent at the higher RH.
It must be noted that any of these concentrations could make a good
print, so what must be sought are the finer nuances. My reference to
drops is the number drops of Li2PdCl4.
A good, solid dark area is found with the 16 drop concentration and
higher. Although the 12 drop concentration is very close. The 8 drop
concentration was definitely slightly weaker, but not due to speed as
the "21-step" did not indicate so. All seemed to have the same speed.
The 24 drop seemed to have more contrast (about ½ stop or slightly
Now, changing eye glasses, the 8 drop print is definitely lacking some
of the details in the shadows.
The 16, 20, and 24 drop prints have the same detail which is only just
barely slightly better than the 12 drop.
This leads me to believe that the optimum concentration is the 16 drops
or at least somewhere between the 12 and 16. The 16 drop concentration
related to a concentration of 24.49%. This would mean a formula as
7.92 g LiCl
16.57 g PdCl2
100 ml H2O
1.98 g LiCl
4.14 g PdCl2
25 ml H2O
[Note: if scale accuracy is 0.01g add 0.02g to the LiCl.]
It is recommended that this new formula be used as more Li2PdCl4 will
not make a difference and less Li2PdCl4 will or may affect print
Summary of conclusions:
Li2PdCl4 should be mixed with the proper balance of LiCl and PdCl2.
Concentration of Ammonium Ferric Oxalate should be 40%.
Ambient relative humidity should be kept above 50% (especially for
Special care must be given to proper humidification of the coating at
less than 50%RH.
Optimum concentration of Li2PdCl4 was determined to be 24.49%.
Disclaimer: (to keep any attorneys happy) This experiment should be
repeated at the 70%RH and other papers may provide differing results.
[Note however that when I optimized the metal salts in the traditional
Pt/Pd process (about 8 years ago), I did so with several papers having
the same result.] Also, 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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