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Firing ScheduleIf you are firing the same thing to the same schedule, it should be consistent in your kiln. There is no one-schedule-fits-all because every project and kiln is different. You can start with the schedules that are published by Bullseye and Spectrum for a general schedule. Or try the schedule below and adjust accordingly. When firing glass in a kiln, there are many variables that will impact your choice of a firing schedule. Here is a list of some of the variables that can affect your outcome. These factors and others will determine the schedule you will use to fire your glass pieces. Each factor is an important and critical part of your firing schedule. Most charts that are provided are based on theoretical schedules only, and are not necessarily the schedule for your particular kiln. They are to be used as guidance and should be adjusted to the specifics of your glass and kiln. Avoiding thermal shock and preventing devitrification are your two main concerns when heating your glass. There are some things you can do to prevent these problems. Devitrification usually occurs between 1300 degrees Fahrenheit and 1400 degrees Fahrenheit. It is a crystalline scum that appears on the glass surface. Rapidly heating the glass through the 1300 degrees Fahrenheit and 1400 degrees Fahrenheit phase will help prevent this problem. Using a devit spray can also help prevent devitrification. Thermal shock is a breakage due to excessive heat differences within the glass. This can be prevented by using a slow rate of heating below the strain point. Your firing schedule should include the following:
Do not look at your glass until it is above the strain point. Once the air is above 1000, it is pretty much safe to look. Always wear eye protection when looking inside the kiln. Glass is generally 50 degrees cooler than the pyrometer reading when heating up the piece, and about 50 degrees hotter than the pyrometer reading when cooling down the piece. Holding or soaking a piece at around 1000 degrees Fahrenheit will help to even out the temperature of the glass. This schedule is a general outline. Remember, there are many factors that go into a successfully fired project (read above). There is no guarantee for your individual results in your project. This will serve as a helpful tool in creating your individual firing schedules. Tack Fuse – The glass layers are slightly melted into each other. Full Fuse – The glass layers melt into each other until they are flush. Slump - Bending glass into or over a mold Once you have a good working schedule for your individual kiln, it should be more consistent in firing. Take good notes to remind you what worked well and what didn’t work. Repeating your mistakes is a waste of time and expensive glass. Experimentation is the best learning tool. Try firing tests with two inch squares of various types of glass, or course making sure they are the same COE. Make samples that consist of 1 layer and 2 and 3 layers. Once you have these samples, mount them on a board with the schedule written on the piece.
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