Last Updated: Aug 10, 2017     Views: 144

Below is the definition of iridescence from the museum's website:

The rainbow like effect that changes according to the angle from which it is viewed or the angle of incidence of the source of light. On ancient glass, iridescence is caused by interference effects of light reflected from several layers of weathering products. On certain 19th- and 20th-century glasses, iridescence is a deliberate effect achieved by the introduction of metallic substances into the batch or by spraying the surface with stannous chloride or lead chloride and reheating it in a reducing atmosphere.

Paul Gardner, in his book The Glass of Frederick Carder, quotes a handwritten manuscript by Carder about Aurene:

This glass depends entirely upon the property of certain glasses being able to keep in solution in an oxidized state salts of the rare metals. This glass when made into articles and subjected to the reducing flame of either gas or oil becomes coated by reduction with a film of the metal, varying in intensity with the proper adjustment of flame. This development requires care on the part of the artist and when the reduced metallic film is sufficiently dense, it is sprayed with a solution of tin salt and then heated in an oxidizing flame. Iridescent colors will be produced, these varying in intensity and color values according to the heat treatment it undergoes.... If iron chloride be sprayed on instead of tin salt, or after spraying with the iron chloride it is followed with the tin salt, a golden color is produced." (pp. 63-64) 

Tiffany's and Carder's iridescent glass was made from different formulas. This article, Louis Comfort Tiffany:  Artistry, Chemistry, Secrecy by Maureen Byko, describes Tiffany's techniques in depth. If you wish to explore more about iridizing glass, I am sending a bibliography of resources. The articles/books range from studio glass to industrial uses. The articles by David Gruenig, for example, provide insight into 20th century studio glass. The video inserted below features curator Jane Shadel Spillman discuss the Blue Arene Vase by Carder:

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