This chapter is about selecting glass for use with the copper-foil or lead-came techniques. See the pertinent sections regarding glass selection for hot and warm work. See Section II and III for information on how to decide what part of a piece of glass to mark and cut.
There are many manufacturers of glass. Beginners should consider using cathedral glass because it is even colored, smooth textured, and easier to learn with. It might even be helpful if the begginer stuck to one of the larger brands of glass for the first few projects since there is a difference in the way each brand reacts to cutting and grinding. Starting out using an expensive esoteric art glass or glass with a radical granite texture could result in poor results and a lot of frustration.
Each glass brand has it's own personality. When you cut glass and break it, there are distinctive sounds you listen for as mentioned in Section II. When cutting glass, if you don't hear any sound it usually means not enough pressure is being used and your not scoring a line. If the glass breaks at all it will be ragged or not follow your desired path. A scrunchy sound followed by a shower of tiny glass chunks means too much pressure. A light scratchy sound means approximately the right pressure. When you break glass, exerting slow gentle pressure on the scored line allows it to "run" and a distinctive yet quiet tone is heard. This tone varies in frequency and sound level from glass to glass. The point is that each glass requires a slightly different touch. Hard glass requires more pressure than soft when scoring and textured glass creates its own kinds of problems.
The prime ingredients for glass are sand, potash, boron, and other addatives that modify the glass for specific purposes. Metal Oxides are used to add color. Temperatures over 2000F are used to heat the ingredients until they are molten in a large pot ot vat.
Plate glass is manufactured specifically to be as flat as possible so that it is optically devoid of personality allowing easy viewing when used for windows. Most plate glass today is made in huge factories on a constant assembly line process. On one end is the mixing equipment and vats for heating the ingredients, the glass is passed over a large vat of molten tin that keeps the glass hot at a constant temperature which allows it to level out by gravity. Then annealing ovens slowly cool the glass so it won't break. Finally the glass is processed by automatic cutting and packing systems.
The kind of stained glass we use today is not manufactured that way. There is more human interaction during each step of the process. Molten glass is typically spooned out onto a hot table with a large ladle where color is added and it is worked into a rough rectangular shape. If it is to have a pattern impressed on it (a texture) it normally passes over a special roller or rollers. It can be hand or machine pressed. The amount of automation depends on the size of the company and the desired effect. Companies like Kokomo Opalescent Glass use very little machinery, other companies are much more automated.
Here are a few glass classifications which are helpful when shopping or discussing glass with others:
The Cathedral Glass as previously stated is a clear, one color glass. Its the kind of glass you can see through unless it has a texture imposed on it.
Opalescent glass is a glass with one or more colors added to a white base, you cannot see through it. This type of glass is sometimes required for lamp making, or where a certain effect is desired. Mixing of cathedrals and opalescent types of glass sometimes provide interesting variations in panels and flat lamps.
Art Glass is glass that traditionally has been hand blown into a large disk or cylinder, it is then cut from the blowing pipe and hand worked. Because of the added labor, it is more expensive and no two batches are exactly the same. Art glass is what is preferred for Tiffany style lamps by purists, although beginners might want to consider opalescent variants on their first Tiffany style project. The German's and French use a method of making art glass that uses a tower-like structure where the glass is draw up the tower. This glass is sometimes called art glass or near-art-glass. Other methods to duplicate this look are sometimes referred to as antique.
Streaky is a glass with more than one color blended into clear glass. Generally you can't see through streaky, or only in snall pathches.
Wispy is glass that is clear and opalescent glass mixed to give a cloud-like appearance. Often it has more transparency than streaky. I sometimes have trouble telling where streaky leaves off and wispy starts.
Ripple is glass that has a roller texture applied that has smallish elongated high and low spots.
Water glass is simular to ripple except that the high and low spots are less prounounced and much farther apart, it looks like rippling water .
Seedy is glass with long thin bubbles trapped inside.
Glue Chip is glass that has glue applied and then removed to impart a texture that looks like window frost.
Iridized is glass that looks like oil film on water, a metalic coating is imparted which has just about every color of the rainbow present.
Baroque glass has a raised swirly texture. If two or more colors are used, the raised swirls usually follow the colors.
There are many other types of glass and textures, many of which are specific to one brand of glass. This is sufficient information for a start.