~~~~~~~~ Excerpt from the Guide to Platinum-Palladium Photographic Printmaking by Jeffrey D. Mathias ~~~~~~~~
No part of this document may be reproduced in whole or in part without the express written permission of the Author.
created October 1999

Testing and Results of prepared Ferric Oxalate Powder

The author has used the Ferric Oxalate (FO) powder manufactured by Bostic and Sullivan (B&S) since about 1987.  This has been an excellent product in both consistency and quality which was regarded as a standard for this test by which to compare other ferric oxalate.

Working solutions identified during the comparison of several FO powders were made.

First, the FO Test described in the guide was run.  The FO behaved as it should and passed test.  This test basically just indicates if it is working in general, or perhaps contaminated, or not of high purity.

Second, tests  for clearing and fogging were performed.  Clearing was complete, with clearing agent and times typically used for the paper selected.  There was no noticeable fogging.

Third, identical prints using FO powder made by Vizcay and this author using Vizcay's process and  B&S were compared (keeping all other things equal).  Prints were made using Crane's Parchment Business Card Stock (AKA: Cover 90) paper.  All prints received identical coating technique (by brush), identical exposure, identical processing using the same negative and a 21-step.
 

Preliminary Prints and Results

Four sensitizer solutions (the Oxalic Solutions and Straight Solutions from the Comparison of FO powders) were used to make prints.
The  solutions were:

Prints from Oxalic Solutions:
A) 16.20 grams B&S FO powder, plus 52.5 ml H2O, plus 0.50 g Oxalic Acid
B) 16.20 grams Vizcay FO powder, plus 52.5 ml H2O, plus 1.40 g Oxalic Acid
Prints from Straight Solutions:
C) 25.9 % solutions B&S FO powder only (no additional Oxalic Acid)
D) 25.9 % solutions Vizcay FO powder only (no additional Oxalic Acid)
Preliminary observations indicated: Aside from the color mentioned, no substantial difference was detected in the prints between Vizcay's FO powder and the standard B&S FO powder.  Difference were noted in that the prints from the Oxalic Solutions were about 1/2 stop slower, had better sharpness, and had better tonal discrimination than prints from the Straight Solutions.
 

Prints and Results from Balanced Solutions

In order to make an accurate comparison, sensitizer solutions were made having the same concentration of ingredients as best as could be determined from the Comparison of FO powders.
The Ferric Oxalate was mixed to a solution strength of 30%.  The metal solutions were mixed as optimized to be used with the 30% FO.   [Formula Calculator of Metal Solutions]

Prints were made using the following solutions of Ferric Oxalate sensitizer.

Prints from Balanced Solutions:
E)  8.45 grams B&S FO powder (contains 0.91 gram Oxalic Acid & 7.54 grams FO)
      1.00 gram EDTA (Na4)
      0.04 gram Oxalic Acid
      H2O to make final volume of 25.12 ml
     (concentrations: 30% FO, 3.8% Oxalic Acid, 4% EDTA)

F)  7.65 grams Vizcay FO powder (contains 0.15 gram Oxalic Acid & 7.50 grams FO)
      1.00 gram EDTA (Na4)
      0.80 gram Oxalic Acid
      H2O to make final volume of 25.0 ml
     (concentrations: 30% FO, 3.8% Oxalic Acid, 4% EDTA)

G)  7.65 grams JDM FO powder (contains 0.15 gram Oxalic Acid & 7.50 grams FO)
      1.00 gram EDTA (Na4)
      0.80 gram Oxalic Acid
      H2O to make final volume of 25.0 ml
     (concentrations: 30% FO, 3.8% Oxalic Acid, 4% EDTA)


Observations of Prints from Balanced Sensitizer Solutions:

  • E, F, & G have the same speed and contrast.
  • The speed and contrast of E, F, & G (Balanced Solutions) is the same as A & B (Oxalic Solutions).
  • E & F have the same color, G may be barely slightly warmer but very close to E & F.
  • The color of E, F, & G (Balanced Solutions) appears slightly more neutral than the color of B & D.
  • The very high tonal values (Zones above IX) in print G seem to be cleaner and have better definition.
  • The dark values of E, F, & G (Balanced Solutions) are the same and are darker/blacker than A, B, C, & D.  Prints from the Balanced Solutions did not show any signs of solarization effect, however the dark values of Zones I and II (where there was no indication of solarization effect in the prints from Oxalic Solutions) were darker/blacker as well.
  • E, F, & G (Balanced Solutions) look identical in all other aspects.
  • E, F, & G (Balanced Solutions) have more sharpness than C & D (Straight Solutions), but not quite as much as A & B (Oxalic Solutions).
  • E, F, & G (Balanced Solutions) and A & B (Oxalic Solutions) have excellent and close to identical tonal discrimination.
    • Additional prints using sensitizer E, F, & G were made on Bienfang 360 and repeated on the Crane paper with a different negative and the 21-step.  Results were identical to and confirmed those above.

    No substantial difference is observed between the Balanced prints E, F, & G, except for the slightly better upper highlight definition found in print G.  The improved upper highlight definition may be related to preparation conditions of the FO powder; further study is warranted.
     

    Conclusion

    Vizcay's preparation procedure allows one to make an unsurpassed, high quality Ferric Oxalate powder suitable for use as a sensitizer with the Pt/Pd process helping produce prints of the highest quality.
     

    Further Study

    Studies are planned to investigate the effects of the amount of Oxalic Acid and pH of the FO sensitizer solution; the threshold of total concentration of the coating mixture, and preparation conditions (including residual HNO3 content) which may affect highlight values.  Other studies of merit could include investigations of other sensitizer solutions and other preparation methods.  The measurement of specific gravity should be improved so as to make an accurate method of mixing known Ferric Oxalate concentrations.
     

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