Last Updated: Sep 29, 2016 Views: 72
According to Virginia Cheffo Raguin's book, the History of Stained Glass, the transparent glass (known as pot-metal glass) is glass that is colored throughout while still in molten form, using colorants such as cobalt for blue and copper for red. These would have been produced in sheets, then split into smaller pieces and used to create the window. In the Middle Ages, they might have been split using a hot iron to start a break. By the 1300s, diamonds were being used to score the glass.
I haven't seen the 'traditional' term before, but maybe it refers to silver stain, a fourteenth century development in stained glass. Known as the only true 'stain' in stained glass, silver stain is a silver oxide which was applied to the back of the glass and then fired, causing the silver to "migrate into the glass", creating a transparent yellow to deep red color, depending on the type of glass, how many times the stained was applied and the temperature of the kiln. Silver stain can even produce green when fired onto blue glass. Prior to silver stain, a reliable method for producing a true yellow color was not available to stained glass crafters.
Enamels, as you noted, would be vitreous material (ground glass and metal oxides) that is suspended in an organic medium that could be "painted" on the glass and then fired to remove the organic material. Enamels were not in widespread use on window glass until the 1500s.
I am attaching a couple of bibliographies on stained glass, in hopes that they might be useful. I hope this wasn't too basic for your purposes---sounds like you are more knowledgeable than I! But I can scan a few pages from Raguin's book or another if you let me know what you'd like.
Thank you for your help. My problem is I decided to study the lesser know areas of stained glass- medieval prior to 1500's and ancient glass. My last project was creating a gold sandwich glass bowl based on a Roman technique. My problem is most sources mention white but don't say how it was achieved. I know opaque white glass for stained glass windows is a recent invention in the history of man putting colored glass in windows, so the question what was used instead. I was told the white color used for faces and other elements was a "clear" glass with a coating of white put on top but can't find anything to prove this. Like I said, most sources I've read just say white without further explanation. Thank you for the research guides. I'm always looking for materials to expand my knowledge. Would it be possible to get a copy of the resource below?
Royce-Roll, Donald. “The Colors of Romanesque Stained Glass.” Journal of Glass Studies, v. 36, 1994, pp. 71-80
I will scan that article and send it out to you! I may even have a pdf copy available, since it is our own publication. I've seen references to a wash that was put on unpainted glass, so I will look back to see if I can find more details about that. Also, would you be interested in posting your question to the stained glass list? It is a fantastically helpful group of experts and all you have to do is subscribe (free) to post. I generally turn to them with my challenging stained glass questions! I can send you the list address if you are interested. I'll be back in touch!