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and modulated laterally, side-to-side. The vertical format demanded a perfectly flat surface for best results, so Edison made his Diamond Discs almost one-quarter of an inch (6 mm) thick. They consisted of a thin coating of a phenolic resin virtually identical to Bakelite on a core of compressed wood flour, later also china clay, lampblack for color, all in a rabbit-hide glue binder. With very rare exceptions, all were about ten inches

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