Several months there was some discussion as to the availability, and
quality of Ferric Oxalate.
Brian Miller [Brian.D.Miller@Dartmouth.EDU] graciously sent me a sample
of the Ferric Oxalate (F.O.) he makes following Fred Foster's recipe. I
ran a comparison with the Ferric Oxalate powder I get from Bostic &
Sullivan (B&S).
The first test was to check for the absence of Ferrous Oxalate which may
be present due to exposure to light or heat or improper manufacturing.
This also checks if the ferric is changing into ferrous. For this I use
Potassium Ferricyanide (PF). By adding one crystal of PF to 10 drops of
Ferric Oxalate no change should be noticed. Then upon exposure to
printing light (conversion to Ferrous) the solution should turn dark
indigo blue.
At the start the Miller and the B&S were about the same yellow color
with the Miller a tiny bit darker. There was slight, but no real green
color to either.
When I added the PF, Miller's immediately turned dark blue. The B&S had
no change. The change of color to dark blue should be an indicator that
the F.O. has been exposed or has gone bad. However, I proceeded with
the next test.
The second test was to check for fogging and clearing. A standard pt/pd
coating mixture is prepared and coated onto a paper that is known to
clear well. Pencil dots applied after drying indicate the edge of the
coating. This is done for each F.O. Both are then put through
processing with no exposure.
Both prints cleared completely meaning that the Miller F.O. had not been
fogged as indicated by the first test.
The third test was to make a print for a negative I have reserved for
these tests. It has a full range of values, large areas of solid and
continuos tones, and areas of detailed lines and texture. This 4x5
negative has been printed onto many paper types and chemical
combinations all stored for reference.
The prints were made on Cranes Platinotype paper (Cranes business card
stock optimized by Dick Arentz)(available from B&S) with a coating
formula of 6 drops F.O.; 1 drop 1/4% potassium chlorate; 4 drops
Palladium salt; 2 drops Platinum salt. Exposure was given by exposing
several coatings at different times. All processing was:
development/enhance in potassium oxalate; pre clear in tap water; clear
in phosphoric acid; wash in tap water.
The final prints indicated that the Miller F.O. indeed worked.
The Miller F.O. required at least 20% less exposure than B&S.
The Miller F.O. also produced a more neutral color and seemed to have a
tad more contrast than the B&S. Although, the contrast difference may
be only a result of the shorter exposure.
Both F.O. had excelent depth and substance.
Both F.O. gave acceptable results. (acceptable to me, critical of
subtleties)
In conclusion:
I would recommend either F.O. for the pt/pd process.
However, please keep in mind that I have not tested the longevity of
Miller's liquid F.O. I have B&S powered F.O. which is seven years old
and works as good now as it did the first day. I do have some of the
Miller F.O. sample left over which I plan to keep for a couple years and
retest.
I am curious and somewhat concerned as to why the Miller F.O. turned
dark blue with the addition of PF. I wonder what other material may be
in the Miller F.O. since Ferric Oxalate will not turn blue with the
addition of PF. I asked Brian Miller why this was so, but he does not
know either.
The following is quoted from Brian's response to me on this inquiry:
"I ran the same ferricyanide test on Fred Fosters FeOx a few years back
& got the same results that you are getting with mine. He couldn't tell
me why it happened so I just accepted it. My FeOx is a blend of stuff
made in a few different ways which seems to cause the ferricyanide
reaction. I suspect that there is some ferrous somewhere in there, but
not enough to cause fogging. I figured out how to make it this way about
7 or 8 years ago & just made it to give me the results I was looking
for. Eventually others wanted the same results. I also find it to be a
bit faster, but not more neutral in tone. I find that it also has a
richer black. I'm not a chemist, so I can't really answer your question,
but I can assure you that there is nothing funky lurking in there... I
hope this helps."
I can accept Brian's reason (or lack thereof), except that I do not
believe that there is any ferrous in Brian's F.O., but rather some other
material which reacts with Potassium Ferricyanide. It would be a good
research effort form someone to analyze the contents of the F.O. I do
not have the time nor equipment.
Hope this information is helpful.
Jeffrey D. Mathias