tartar

1 :  an incrustation on the teeth consisting of plaque that has become hardened by the deposition of mineral salts (such as calcium carbonate)

2 :  a substance consisting essentially of cream of tartar that is derived from the juice of grapes and deposited in wine casks together with yeast and other suspended matters as a pale or dark reddish crust or sediment; especially :  a recrystallized product yielding cream of tartar on further purification