The use of zinc sulphide as an opacifier, with some notes on the results of attempts to produce luminous enamels
A 1920 master's thesis by Robert Twells at the University of Illinois on zinc sulphide as an enamel opacifier and on attempts at luminous enamels, written for ceramic chemists and industrial enamellers. Its plates are gridded photographs of small rectangular test tiles, labelled Series I-III and Reducing/Oxidizing, showing speckled, blistered and mottled surfaces usable as grain, spotting and blotch textures.
