What is a drop out fuse?

A drop out fuse is a type of slump fuse where the glass is placed on a ring with an open center that is supported by blocks to create an inside area for the glass to "drop" into. The glass usually starts out as a round flat "plate" of glass that has been full fused, or fused to around 1500 degrees where the layers of glass become one solid piece. The glass is placed so that the outside edge of the glass, is just inside the outside edge of the ring. The glass is then fired to slump temperatures, around 1300 degrees or to the temperature where the unsupported glass on the inside of the ring will begin to flow down into a bowl shape and held there until the desired drop is achieved.