No worries, I understood your previous comment. It's fine that you haven't tried it, but your understanding of chemistry is probably better than my own. I will have to try it myself, when my accommodations allow. I am a science fiction author and am writing a new series where authenticity is important. The least I can do is take some time to research the material I'm writing about so it's not blatantly wrong.

Thanks for the clarification. Looking at the solubility of calcium hydroxide (0.066 g/mL) vs. potassium hydroxide (162.9 g/100 mL) --This is for a solution at boiling 100Celcius -- I imagine it would be possible to simply boil off the water from the solution. Basically, using recrystalization as a purification technique. The Calcium hydroxide would be forced to precipitate, and then the solution containing the potassium hydroxide could be poured off. Does that sound reasonable?

Great information, thank you. About the comment "Calcium should not be part of soaps," I believe you mean the act of adding CaCO3? If you use that method to get from potassium carbonate to hydroxide, after precipitating, I was under the impression you would have 2 KOH + CaCO3, and all the CaCO3 would settle out of the solution. Is this incorrect? Where does the insoluble soap scum come from?