COE

Coefficient of Expansion

When thermal energy is applied to a substance, let's say glass, the energy between the bonds increases and the result is an extension of the bond length. Usually, when a substance cools, it will shrink, thus the bond lentgths are shrinking, and vice versa for heating. Thermal expansion and contraction can result in two types of expansion, linear and volumetric.

COE and Glass

Each type of glass that is varied upon its molecular composition will result in a different COE. Although one could create two substances that have identical thermal expansion profiles, glass is typicaly catagorized via it's COE.

These are some major groups of glass that lampworkers typically come across:

• COE 32/33: Most industrial borosilicate
• COE 84-87: Common float glass
• COE 90: Most Bullseye glass
• COE 96: Most spectrum glass
• COE 104: Moretti

Compatability

There are variou types of metals and other compounds that are compatible with borosilicate. Gilson opals, silicon are some examples. Some materials can be semicompatable, such as some sparkle colors do not like to be encased deep in a marble or vessel. This can be avoided by using these colors on the surface, not encased deep, or a glass worker with a massive amount of experience with a color will know the limitations of the materials. Bad batches of colored glass rod is notorious for cracking problems, most likely an incompatability of thermal expansion.