Exact formulas for this compound varied by manufacturer and over the course of time, but it was typically composed of about one-third shellac and about two-thirds mineral filler, which meant finely pulverized rock, usually slate and limestone, with an admixture of cotton fibers to add tensile strength, carbon black for color (without this, it tended to be a "dirty" gray or brown color that most record companies considered unattractive), and a very small amount of a lubricant to facilitate mold release during manufacture.