Potassium Oxalate is the standard developer for platinum & palladium printing (Pt&Pd) and it’s much cheaper to mix yourself than buy readymade powder. Its expense is in the production, not the cost of the two ingredients. Both are relatively inexpensive but potassium carbonate is alkaline, oxalic acid is acidic. Mixing these in solution creates substantial effervescing, it takes time to make. It’s expensive to manufacture.
METHOD AND PROPORTIONS TO THE MIX 1 LITER OF POTASSIUM OXALATE
Dissolve 220 grams of potassium carbonate in 900 ml water at 100°F/ 38°C
Very slowly add 195 grams of oxalic acid to the potassium carbonate solution. There will be intense effervescing. Continue adding smaller amounts of potassium carbonate until the reaction stops, there’s no more fizzing.
The pH is important. The developer will not work if the pH is 7 or higher. Litmus paper is available at pharmacies but usually only for the full pH range, 0-14. Chemical suppliers sell pH strips in narrow ranges, buy a packet in the 4.5-7 pH range. Add oxalic acid with stirring until a pH of 6.5-6.8 is reached. Hitting anything closer to 7 is like treading a moving needle.
The goal is a super-saturated solution of Potassium Oxalate at pH 6.7.
As the developer is used it’s important to maintain a minimum pH of at least 6 for contrast and tonal seperation. Check pH after twenty 8X10”, 20,3X25.4cm prints. Sprinkle small amounts of potassium carbonate to bring the pH up to 6.7.
MIXING SUGGESTIONS
Always use a much larger container than the volume of solution mixing any solutions. I recommend mixing 3.5L as it takes the same amount of time and lasts much longer. 10L to 15L plastic containers are found at hardware and agriculture suppliers.
Use inert (non/reactive) mixer rods, plastic or glass.
Shop around for chemical suppliers as the prices vary substantially. Buy technical grade.
This compound is poisonous. Oxalic acid causes liver failure if ingested. Wear rubber gloves and goggles.
Clean equipment and surfaces when finished.