Answered By: Aprille Nace Last Updated: Sep 17, 2016 Views: 12
W. A. Weyl's book, Coloured glasses [Sheffield, England: The Society for Glass Technology, 1976] is the standard resource for color theory. Under "black glasses" in the index, Weyl lists: chromium, pp. 137, 143; cobalt, p. 188; phosphide, p. 326; selenium, p. 323; sulphide, p. 280; titanium, p. 216; uranium, p. 207. Also: Black glass (defect), p. 241, 267; black-out window glass, p. 227. Don't miss his thorough introductory chapters.
A collectors' definition of black glass (from David Shotwell's Glass A to Z) is: "1) Glass that is black in color, made using manganese oxide, blended with iron oxide, in the batch; 2) A very dark green, brown, blue, or purple glass that appears black under normal lighting conditions; the true color determined by placing it between an intense light source and the observer." p. 41.
Black may be obtained in many ways, as is evident in Weyl.
Charles Bray briefly discusses manganese as a means to get black glass: "Used in proportions 1% to 10% to give a range of colors from pale purple to black in a potash glass; tending to pink shades in a soda glass. It also has a strong tendency towards stiffening the glass and making it difficult to work. It was often used to produce a pale decolorizer to counter the color resulting from iron in the batch materials. It is very sensitive to variations in the furnace atmosphere." p. 74 Dictionary of Glass, Materials and Techniques.
His Ceramic and Glass: A Basic Technology provides a little more information.
Henry Halem's website addresses the basics of coloring glass: http://web.archive.org/web/20070209093509/http://glassnotes.com/culletcolor.html