Clay vitrification occurs at temperatures higher than 1200 degrees fahrenheit (f). Clay becomes vitrified when heated above its melting point (1200 f). This process happens quickly as clay's molecules begin moving faster than they normally do at lower temperatures because they are being pushed by their neighbors' movement toward each other as they become hotter; this results from heating above its melting point (1200 f) until all molecules move together as one solid mass called "clay". Clay then becomes very hard like glass!