Most fusing methods involve stacking, or layering thin sheets of glass, often using different colors to create designs. The piece is placed in the kiln and then heated to temperatures up to 1500 degrees until the separate glass pieces bond together. The amount of time and temperature vary depending on the design. After a piece reaches the fusing temperature, it must sit at various stages to make sure the glass process is finished and that it is sturdy and dishwasher safe. This process is called annealing the glass. The entire process can take up to 12 hours.
Designs generally require multiple firings: one to fully fuse the glass, additional one or two firings to add design elements and dimensionality, and a final firing to mold it into the shape it was designed for. This final process is called slumping which allows the creation of larger, functional pieces like dishes, bowls, plates and trays.
It is not known for sure when or where glass fusing techniques began. There is evidence that the Egyptians were familiar with rudimentary techniques and some historians believe that the earliest fusing techniques were developed by the Romans. Glass work enjoyed a revival during the Renaissance Period, although fusing was largely ignored during this time. Glass fusing became popular in the early part of the 20th century and particularly in the U.S. during the 1960s. Modern glass fusing is a widespread hobby but the technique is not widely used for large-scale glass ware production.