Potash, an essential raw material of the 18th century, used to be produced from the ashes of plants. Known since antiquity, it was in 1807 that Humphry Davy put an end to the decades-long controversy about its nature as a compound. The technology behind potash production was implemented in Brazil by the Portuguese naturalist Frei Velloso. The steps in potash production and the related difficulties and controversies about its composition make this case study a convenient tool for teaching the history of chemistry. The results concluded that the potash production from ashes provided proper context for teaching practical extraction yield, carbonate identification, and pH determination.