Last Updated: Aug 10, 2017     Views: 38

Engraved Bottle in Gold Ruby Glass with Metal Cap,             
Germany, about 1700. 2011.3.178
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From Dr. Robert Brill, Research Scientist Emeritus:

Purple of Cassius is a suspension of metallic gold particles that can be added to a batch as one means of introducing gold into a glass.

Purple of Cassius is an additive used to color glass red.  It is not a catalyst.

Strictly speaking, the metallic gold is suspended in what is called a solution, but the metallic particles of gold are not a part of the solution.  They are just floating around in it.  The particles are so small that they do not settle out under the force of gravity, they remain suspended and drifting around in the liquid.

The whole thing (the solution of other stuff with metallic gold particles suspended in it) is an additive.

Information on our previous exhibition called Glass of the Alchemists, as well as the book Glass of the Alchemists by Dedo von Kerssenbrock-Krosigk c2008, discusses the use of adding purple of cassius to glass. The page on Gold Ruby Glass speaks some about the use of Purple of Cassius.