Somewhere in the past I learned that a percent solution is based on the number of grams of a chemical in a given amount of water. Therefore, a 1% potassium carbonate solution is made up of one gram of potassium carbonate in 100ml of water, or 10grams of potassium carbonate in 1000ml of water. Many photograhic texts continue to describe a percent solution in this way.

From the discussions on this topic last year on the alt-photo-process list I learned that chemists describe the term percent solution in a different way, so that 100g of potassium carbonate in 100ml of water is not exactly a 100% solution. However, I have no practical way of adopting the measuring system of the chemicsts so I will continue to refer to the Pyrocat-B stock as a 100% solution of potassium carbonate.

It is possible to substitute sodium carbonate for potassium carbonate with Pyrocat-HD. To do so, prepare a 20% stock solution of sodium carbonate, i.e. 20g of sodium carbonate in 100ml of water. To prepare a working solution dilute 1 Part A + 5 Parts B + 100 parts water. This working solution will have working qualities very close to the 1:1:100 dilution made up from a 100% potassium carbonate stock solution.

Potassium hydroxide will also work as the accelerator but my tests indicate that its use results in slightly larger grain than the carbonates.

Sandy King