Edison had introduced wax cylinders that played for nominally 4 minutes (instead of the usual 2) in 1909 under the "Amberol" brand. They were made from a harder (and more easily breakable) form of wax to withstand the smaller stylus used to play them. The longer playing time was achieved by shrinking the groove size and spacing them twice as close together. In 1912, the Edison company eventually acquired Lambert's patents to the celluloid technology, and almost immediately started production under a variation of their existing "Amberol" brand as "Edison Blue Amberol Records". These new celluloid recordings were given a core made from plaster of Paris. The celluloid material itself was blue in color, but purple was introduced in 1919, "... for more sophisticated selections". The use of camphor in Edison's celluloid base rendered it more stable, and the plaster core provided further resistance to possible shrinkage, but the playing surface is still liable to split if stored in less than ideal conditions; however, the groove pitch rarely changes. The plaster core itself can deteriorate in conditions that are too damp or too dry. Nevertheless, most Blue Amberol cylinders are, today, quite playable on antique phonographs or modern equipment alike (although the plaster core may need some reaming).