in the glass-trade, a sort of potashes imported from Spain, inferior in goodness to that of the Levant; called polverine, when loose, small, and in powder; and rochetta, when in hard rocky lumps.—The frit made of these makes fine and clear crystal glass, especially that from the rochetta, or the polverine in lumps; but the barillia of Spain, though it be usually fatter, yet makes not a glass so white, but usually inclining a little to a bluish colour.