Potassium carbonate is an additive for cold process liquid soap (liquid soap without any heat besides the exothermic chemical reaction of saponification). -- it makes the soap base easier to stir during the cook and helps speed things up during the dilution phase.
INCI: POTASSIUM CARBONATE
Use: 2% - 2.5% per pound of soap
Add to lye solution
Thoroughly dissolve 2% Potassium Carbonate in hot lye solution. If you choose this option, you will need to add 1.7% Borax or Citric Acid to your dilution water to neutralize the Potassium Carbonate.