From Stained Glass Step By Step, by Patricia Ann Daley:
I love this book for its plethora of information, from the process of making glass to types of glass to leading and foiling methods of assembly. The projects focus on different types of assembly. A list of projects includes: a Fleur de Lys Panel (Lead Came Method), a Butterfly Sidelight (Copper Foil Method), a kitchen wall clock, a mosaic-ed vase, a six panel lamp, and an Alaskan Totem Light (Sculptural Element).
The first 10 page chapter tells about the process of glass making, as well as describes the different types of glass...
First and foremost, glass is a liquid. Mind you, it's a solid liquid, because it moves so slowly that we don't notice it. However, if you were to examine a large cathedral window that has been standing upright in the same position for many years, you would notice that at the bottom, the glass has flowed downward and become thicker.
Glass is made from silica sand with 1% iron, soda ash, limestone and borax, plus added metal oxides for color: dichrome=green; copper/cobalt=blue; cadmium=lighter reds, oranges, and yellows; gold salts=deep, rich reds, gold pinks and purples.
Generally, most glass that is on the market today is machine-made. The process begins with a carefully measured dry mixture that is place in a crucible, a large "bowl," and then placed in a furnace to slowly heat the mixture to white-hot temperatures. After reaching the high temperatures, the glass liquid is ladled onto mixing slabs where the glass is twirled with a two pronged fork, similar to the way salt water taffy is twirled to mix it. The color changes to a bright orange and the consistency resembles taffy as the glass begins to cool.
The glass is now ready to be rolled, and this is the point where it is textured. The bottom roller gives the texture to the glass and is engraved with the texture. For standard glass, the thickness is now at 1/8" and the color of the glass mixture becomes a dull orange/red as it has cooled even more.
At this point the glass enters the annealing lehr, a conveyor line that slowly cools the glass by moving it from the hottest end of the "oven" to the cold, room temperature side. The glass is ready to be cut and packed into crates for distribution.