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“The process for making these glasses is quite simple. Sulphur, or an alkali sulphide, is dissolved in molten borax, and into the brown melt excessive boric oxide or phosphoric oxide is stirred. The color changes at first to dirty yellow, then to Grey and finally into a pure blue. This blue color being due to elementary sulphur cannot be obtained in glasses which contain major amounts of zinc, cadmium, or other ions of heavy metals with a pronounced affinity for sulphur.”
-Coloured Glasses, Weyl, pg. 258
Sounds like a fun, if stinky, experiment if nothing else!
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