Ed Bush of Painted Post, New York tells us the chemical differences between Tiffany and Carder’s iridescence.

Alan,

In the last Gazette Gerry Eggert stated that there must have been something different in Tiffany’s and Steuben’s procedures in producing the iridescence of their products. The following sentence appears in the article “The Technology of Tiffany Art Glass” by W. D. Kingery and PB Vandiver, referring to the iridescent coating on Tiffany’s products: “Tiffany’s patent stipulates the oxide [tin and iron oxides] be applied by heating chloride crystals rather than by spraying with an alcoholic solution as is now more common and probably was done by F. Carder.” Tiffany’s process worked because of the high vapor pressure of stannous and ferrous chlorides at fairly low temperatures. For example stannous chloride melts at 246 degrees C. and the liquid boils at 623 degrees. In Greg Merkel’s talks on iridescence he has discussed these two processes.