A major issue when fusing glass is the COE or coefficient of expansion. When glass is heated in the kiln it will expand and it will contract as it cools. Two pieces of glass being fused together must have a compatible COE to create a successful piece of art glass. The expansion and contraction happen at a molecular level and may not be obvious to the naked eye but the stress of fusing incompatible glass may result in breakage during the firing process or 6 months down the road. I use COE 90 glass for my jewelry. There are numerous fusing glass choices with different COE. I am very careful to check the COE before purchasing new dichroic glass. It is important to me that when a customer buys my dichroic fused glass jewelry they can feel confident that it will last. If you want more information about glass fusing and COE you can check www.warmglass.com  for great tutorials.