Potassium Ferricyanide: Fantastic or Frustrating?
By Jon P. Fishback
I recently saw a formula for a working solution of Potassium Ferricyanide (PF) and instructions for its use, in an internet discussion group. It went something like this: Dissolve one (1) teaspoonful of crystals in two (2) ounces of water. Use a que-tip to apply the solution to the highlight areas of the black and white print.
This formula and instructions is a recipe for frustration and an incredible loss of photographic paper. I know this, because many years ago I was given similar instructions and turned loose in the darkroom. Thirty-five years, much frustration and wasted paper later, I have come here to clear up the PF mystery.
Potassium Ferricyanide acts as a bleaching agent to the highlight areas of the black and white print. This is the truism that most people subscribe to. The fact is, PF bleaches all areas of the gelatin silver image. It just works faster on the areas that have the least un-dissolved silver -- the highlights. Right now I will discuss its use to bring up highlights only. PF works in conjunction with hypo and will not function without it. PF is not an easy substance to use. It is volatile and make itself painfully obvious on the print, when not handled properly.
The only formula that I know of is for the stock solution and the stock solution is not used full strength for anything. The stock solution is very simply a saturated solution. That is, distilled water (120 degrees Fahrenheit + or -) and PF crystals, stirred until it will not dissolve any more crystals. Filter it and it is ready to use. After this, it all depends on what you want to do with it. The formulas are up to you.
This is where the experimentation starts. There are several methods of using PF. I will begin with the most traditional. In a small plastic tray, similar to the type used by watercolorists to mix paint, place two drops of PF stock solution with ten or fifteen drops of distilled water, and one drop of wetting agent. Use a scrap print that has good highlight and shadow detail, one that has been fixed but not washed. Place the print on a piece of glass and work over the sink with the water running. (The running water is your safety net. If you see the highlight coming up too fast, get it under the water fast.) Wipe the excess hypo off the print with a paper towel. With a small bristle brush, paint the solution on the highlight area of the print and watch very carefully. If you can see the highlight area getting lighter, you are working too fast and the solution is too strong. Wash the print under running water for a few minutes and put it back in the hypo to soak.
It Comes Out In The Wash
If you do not wash the print, you will carry PF into the hypo tray and accelerate the bleaching action, not to mention ruin your hypo. Put a few more drops of water in the PF solution and try again. You are working at the correct dilution when you must apply the solution five or six times to the area before there is any discernable change in the highlight. When the highlight looks right, do not place the print back into the hypo. This will accelerate the PF and you may end up with a lighter highlight than desired. Place it immediately in the wash water. When the print is dry the highlight should be enhanced but not obviously. No one should be able to tell the print is not a straight print.
The second method involves enhancing a washed print that does not have any residual hypo in the emulsion. Add five drops of hypo to the dillution above and follow the same steps, eliminating the hypo tray. Simply wash the print for a few moments under running water, between applications of the PF/hypo solution. PF is very unstable when mixed with hypo and will exhaust itself in the tray. If you are going to work for extended periods, you must prepare fresh solution at regular intervals. Remember, the fresh solution works faster than older solution.
Once you have mastered the technique of raising the highlights of your prints selectively as above, you may want to try using the tray method to raise all the highlights of the print at one time. This is one of the trickiest methods to master. Start out with a few drops of PF in a tray with sixteen ounces of water. After the print has been fixed thoroughly, without washing, place it quickly under the PF solution and constantly agitate it under good light. Watch carefully and when it looks right, get it out and under the running water. Again, the solution should only be strong enough to change the highlights during several applications. Any faster than this and it will be too hard to handle. If you are doing this properly, you will need to re-soak the print in the hypo tray several times, so remember to wash off the PF before placing it back into the hypo tray. PF working any faster than this is too hard to handle.
All Together, Now
If you have been paying attention you will already have figured out that you can put hypo, PF, water, and wetting agent together in a tray and work with a washed print. This is the hardest method of all to handle and should only be attempted after the other two are mastered.
Properly used PF is an exciting tool that will enhance your prints. Improperly used it will ruin your work, frustrate you, and cost you unnecessary loss of paper and chemicals.
If you wish to study two masters of the use of Potassium Ferricyanide, study the work of Karsh and William Mortensen.
About the author: John Fishback has been a photographer for over 40 years. He has taught photography at the college level and published numerous articles on photography, and his black and white work is part of the Seattle Art Museum's collection.