Glass fusing is a process where you layer several pieces of glass and heat it in a kiln to between 1200 and 1500 degrees Fahrenheit until the layers melt, or fuse, together. The final temperature and the length of time the glass is in the kiln determine the final shape of the piece. A single kiln run lasts between 5 and 14 hours, depending on the complexity of the item. Most of my pieces of jewelry require two or three firings.