Take your vegetable matter, and char it with fire until blackness is obtained. Add more heat, and continue until the blackness changeth to gray. The gray stage is fine, and the salts will extract without a problem at this stage. However, it's possible to further calcine your vegetable matter until whiteness is obtained. This represents the purification of the impure body by fire. Only that which is essential to the body is left after the body has been freed from its various superfluities. This body contains salts of a dual nature, and can be subjected to two manipulations.

First we extract the water soluble salts: Take your ash, add an appropriate amount of distilled water, and boil for 15 minutes. Allow to cool, and then filter, or decant. Extract the ash material three times. Pool all extractions. These can be evaporated to obtain the dry salts. The evaporated dry salts, if slightly colored, can be subjected to further calcination to obtain pure white salts. These are mostly sodium/potassium carbonates.

Second we extract the water insoluble salts with acetum: Take the ash material (after the water soluble salts have been extracted), add distilled acetum (regular white distilled vinegar will work fine - 6%), and boil for 15 minutes. Allow to cool, and then filter, or decant. Extract the ash material three times. Pool all extractions. These can be evaporated to obtain the dry salts. By the action of acetic acid the insoluble salts were converted to their soluble forms. These are mostly magnesium, and calcium acetates.

Solutions of these two salts can be added together to produce a precipitate per se (without superfluous addition of a generic alien alkaline body - i.e. lye, caustic potash, etc).

Pictures of this process will be added soon!