Tartar accumulates as a hard crust on the inside of wine casks as fermenting grape juice loses solubility for its own natural acid salts while the alcohol content rises, precipitating out a reddish or yellowish deposit that winemakers scraped and sold as a raw commodity, the crude material called argol. It was not, in its crude state, considered a laboratory reagent so much as a starting material: chymists purified it by repeated dissolution and recrystallization to obtain the whiter, purer form known as cream of tartar, and burned it in open fire to ash to obtain salt of tartar, a genuinely useful alkaline salt. Tartar's distinctive sharp, sour taste and its origin from fermented wine rather than from a mine or a metal marked it out, in the classification schemes of the period, as belonging to a different family from the mineral salts and vitriols, an organic acid salt long before organic chemistry existed as a discipline to name it.
Beyond its role as feedstock for salt of tartar, purified tartar found use in dyeing as a mordant and in medicine as a mild laxative and diuretic, uses that persisted into the modern era under the more familiar name cream of tartar, still found in kitchens today for baking and candy making, where its acidity stabilizes egg whites and prevents sugar crystallization.