POTASSIUM CHLORATE
Adding Contrast to a Platinum/Palladium Print
PRACTICAL
Mix a 1% solution of potassium chlorate by disolving 1gram in 100ml distilled water. Add for contrast as you would traditional sensitizer #2. Make up the difference of lost ferric oxalate by adding more sensitizer #1, ferric oxalate.
Sensitizer #2 is added to increase contrast in platinum and palladium (Pt/Pd) prints but traditional sensitizer #2 is a self-destructive compound. Ferric oxalate is a reducer, potassium chlorate is an oxidizer. They will begin reacting with each other as soon as they are combined. Isolate the potassium chlorate until the moment of making a print.
Sensitizer #2 rubber bulb that burst after not being used (gas released) for three months.
THEORY
The ability to control the contrast of a print is essential, this is where the artistry of printing lies. Ansel Adams compared making a print to a musician playing sheet music. The analogy is the negative is fixed, the sheet music but how the printer interprets the image is flexible and interpretive.
Traditional sensitizer #2 is a reactive compound. Ferric oxalate is a reducer, potassium chlorate is an oxidizer. Although this reaction is very slow compared to other oxidizers, it still occurs. The chlorate and iron will be less effective as both will have already yielded oxygen atoms and ions. Optimum blacks will be lost and as will clear, crisp separations in high lights. This reactive event should not happen until the print is ready to be exposed. Separate potassium chlorate by mixing it in distilled water without ferric oxalate. It can be mixed in any percentage but commonly a 1% solution, 1gram pot. chlorate to 100ml distilled H²O. If you’re making smaller prints (4” X 5”, 10.16cmX12.7cm) use a .25% solution for more subtle control. Oxidizers increase contrast because they restrain the reduction of these three metals. I recommend potassium chlorate for its effectiveness and stability. There are many variables in hand-coating paper and chemical stability helps achieve predictable and consistent results. If potassium chlorate is isolated from other compounds it is remarkably inert, unlike other oxidizers such as hydrogen peroxide. There are other oxidizers I’ve tried but I never found a significant difference or benefit.
OXIDIZERS ARE DANGEROUS
All chemistry should be handled with care and respect. Oxidizers can be explosive when mixed with other compounds. Potassium chlorate was the original primer used in manufacturing gunpowder. Never mix pure crystal potassium chlorate with powdered metals, particularly silver nitrate.
Oxidizers with excessive oxygen atoms, such as dichromates, are carcinogenic. Use with great caution if at all.