About Fused Glass
THE FUSING PROCESS
Full fusing, the complete merging of two or more pieces of glass into one, takes place at around 1500 degrees F. Above that temperature, glass becomes increasingly liquid
The "heating" phase, which takes place between room temperature and around 1200 to 1700 degrees F (depending on the process you are performing), is where the glass makes the transition from a solid to a more flowing form. As glass is heated and moves through this phase, it goes through three separate states. First, from room temperature up to about 1000 degrees F (540 degrees C), glass remains rigid and brittle. It is expanding slowly, but will still crack or break if the temperature increases too rapidly.
By the time the temperature of the glass gets above 1000 degrees F, any glue, moisture, or surface contaminants have burned off. The glass begins to soften slightly and the surface of the glass will look glossy
When the temperature reaches around 1300 to 1400 degrees F, the glass gradually becomes soft enough to conform to a mold. It starts to glow a bright yellowish-red. The edges may soften and round and two pieces of glass that are touching will begin to stick together. This is the temperature range where slumping takes place
If heating continues above 1330 degrees F and moves toward 1500 degrees F (820 C), the color of the glass deepens and becomes more red. Glass in this range has slumped completely and even starts to stretch out of shape.
Full fusing, the complete merging of two or more pieces of glass into one, takes place at around 1500 degrees F. Above that temperature, glass becomes increasingly liquid.
Annealing is a process by which the stress in the glass is relieved and the molecules in the glass are allowed to cool and arrange themselves into a solid, stable form. Successful annealing is the key to creating glasswork that will remain stable once it cools to room temperature
Once annealing is complete, the Cooling to Room Temperature phase begins. Often this is no more complicated than simply allowing the kiln to cool naturally, but thicker pieces of glass and kilns that cool rapidly require a bit more attention. The key is to slow down the rate of cooling so that thermal shock is prevented and the glass cools without cracking.