DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph (SEM) of Surface recording grooves of a 78 rpm phonograph record. Early disc phonograph records (also called gramophone records) were made of various materials including hard rubber. From 1897 onwards, earlier materials were largely replaced by a rather brittle formula of 25% shellac, a filler of a cotton compound (similar to manila paper), powdered slate, and a small amount of a wax lubricant. Vinyl (polyvinyl chloride) was used as a 78 rpm record material starting in 1940. These records had much less noise and less ability to break. A phonograph record is an analog sound storage medium consisting of a flat disc with an inscribed modulated spiral groove usually starting near the periphery and ending near the centre of the disc. Magnification: x19 when shortest axis printed at 25 millimetres.
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