I'm trying to get more concrete information about the chemical process of creating soap from wood ash.
What I’m confused about: Many soap-making materials say that you create potassium hydroxide directly from filtering water through wood ash. As far as I can tell this is false? You are actually getting potassium carbonate (and some small amount of other residue.)
To create potassium hydroxide from this, historically you would add a solution of calcium hydroxide (calcium oxide/burnt limestone dissolved in water). Calcium carbonate would precipitate out of the solution, leaving behind potassium hydroxide. From my understanding, a lot of modern soap-makers are simply misunderstanding the chemistry, or not realizing that the lime has to be added before they actually have potassium hydroxide.
However, some sources say that if the wood is heated hotter and given a more complete burn, thus combusting more of the organic material, then more hydroxides will be dissolved instead of carbonates, thus negating the need for lime. Is this true?
I have also read that if you take the potassium carbonate, dehydrated, and heat it to an (uncertain) degree, it will burn off carbon dioxide and create potassium oxide, which added to water will become potassium hydroxide. Is this true? How hot do you need to burn it, if so?
However, other sources say heating potassium carbonate only purifies it, creating pearl ash, which is still potassium carbonate.
Basically, I just need more information about potassium carbonate vs. potassium hydroxide from wood ash sources.