The first thing to remember when fusing dichroic glass is that like all glass used in glass fusing, it must be compatible. Normal windows or float glass are generally incompatible, so they should be avoided.
Take a look at some glass suppliers and explore their selection of patterns. Next to the description, you will see that each piece of glass has a COE number, usually 104 or 90.
You must fuse the glass with glass of the same COE and you must not cross them. The mixing of COE results in breakage as the glass expands and contracts during the cooking process.
The COE, or coefficient of expansion, is simply a measure of the degree of expansion that the glass goes through as it heats up. Dichroic glass can come on a clear or black base. Over black can be used as a base. A darker base is best used over a darker base as the coating can become almost invisible in sunlight.
If you are using more than one layer of dichroic glass, you must remember that the coated sides should not touch each other. Remember that the coating is a metal oxide. Having two of these directly connected means the glass cannot be fused together properly, resulting in ruined patterns of warped glass.
This glass can be used as an inner layer or as a top layer, without covering. If left uncovered, the coating will give a metallic finish and is fairly scratch resistant. Uncooked, the coating must be handled with care as prolonged exposure to water can ruin the coating and is extremely susceptible to scratching.