Interesting....
http://www.museumofglass.org/education/learn-about-glass/science-glass/
There are several ways to impart color into glass. Most color is created by mixing a specific oxide into the batch and allowing it to react with the other constituents during the melting process. The results depend on a good number of variables, some of which you have control over and some of which you don’t. There is still a tremendous amount of trial and error going on in the field of colored glass chemistry as we develop new glasses and try to nail down what does what, and “Can we do that again?” Or, “I hope we never make that mistake again!” It is not surprising that only a small percentage of glassworkers make their own colors. Batching and melting color takes time, money, space, and extensive knowledge of glass chemistry. There are some serious health risks to think about as well.
Most glassblowers today use a pre-manufactured form of concentrated color that is compatible with the clear glass that they are melting in their furnace. These “pigments” that are specifically formulated for applications in hot glass. The colors come in every color of the rainbow, either are transparent or opaque. Olympic Color Rods is a glass supply company that carries the Kugler© color line that is used in the Museum of Glass hot shop.
Color is manufactured into rod, frit and powdered forms, and can be applied in a million different ways (or more). That’s the fun part. We get color from “Reichenbach”, “Kugler” and “Zimmermanni” in Germany, “Gaffer” from New Zealand and “Flying Colors” out of New Mexico just to name few (they are the glassblowers version of “Crayola” crayons). Here’s a run-down of the most commonly used colorants. The bulk of them
may be found on the periodic chart #’s 23-29, with #’s 47,48,50,60,68,70, and 92 offering additional color possibilities.
Cobalt (CoCO3) – a very small addition of cobalt carbonate will turn your melt a deep dark blue, thus creating the all-time best selling color for glass blowers, cobalt blue. Other blues can be achieved with copper.
Chromium (Cr2O3) – adding this to the melt will yield an emerald green color
Copper (CuCO3) – Copper is one of those freaky chemicals that react quite differently with the other constituents of the melt. It is also highly susceptible to the atmospheric conditions of the melting chamber. So, depending on how you melt it, and with what, you can obtain: blues, greens, and even some tasty ruby reds (or if you’re off by a fraction, a nauseous liver-brown).
Manganese (MnO2) – chemists refer to this as a fugitive colorant. It gives rise to: purples, blue/violets, and some browns. Can also be affected by sunlight and U/V.
Silver (AgNO3) – can yield a variety of colors, from yellows to blues, and a wild mix of others depending on how you introduce it to the melt.
Gold (AuCl3) – the most beautiful ruby-red you may ever see. (a.k.a “granny-grabber pink” for its inherent ability to attract a certain member of our society) Gold must be introduced in a chloride form, and it too is very tricky to melt.
Iron (Fe2O3) – greens and browns
Cadmium Sulfide (CdS) – oranges, also a challenging color to melt.
Cadmium selenium (CdSe) – deep ruby reds. Another tricky color to melt, in that the right temperature and atmosphere must be present in the furnace otherwise it will turn livery/brown.
