to discover that spark testing can be used reliably to classify ferrous material. He originally claimed to be able to distinguish different types of ferrous materials based on percent carbon and principal alloying elements. Moreover, he claimed to achieve an accuracy of 0.01% carbon content. Tschorn produced an exhaustive treatment of spark testing. His book, Spark Atlas of Steels, along with Spark Testing by Gladwin represent the two most comprehensive texts on the subject As of the late 1980s, the industrial use of spark testing is not as common as it used to be. In the early 21st century the availability of portable X-ray fluorescence equipment largely superseded it in laboratory practice. See also Flame test Emission spectrum References Bibliography . . . . . . . . . . External links Spark test pictures of various materials Ferrous alloys Metalworking