Origin: earlier in pl., potashes < Du potasschen < pot, pot + asch, ash: orig. prepared by evaporating the lixivium of wood ashes in iron pots
See potash in American Heritage Dictionary 4
Origin: Sing. of obsolete pot ashes
Origin: , translation of obsolete Dutch potaschen (from the fact that this substance was originally obtained by leaching wood ashes and evaporating the leach in a pot).
Learn more about potash