"Probably the second most asked question is....."How do you make different colors
?". That can be done by adding the precise amounts and combinations of various metal oxides. With Cobalt Oxide you get blue, with Iron you can get green, with Gold you can create a beautiful cranberry colored glass.(and a rather deep hole in your wallet) The coloring agents we will be using for our Ruby are Cadmium and Selenium. "

How colored glass is made:http://www.ironandglass.com/howglass.htm