Keeping accurate notes on your firings will help you determine your future firing schedule. There are no exact rules with heat work. Every kiln is different and unique.
If 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.The heating pattern of the kilnThe accuracy of the temperature recording deviceIf the kiln is a top fire or side fire kilnLocation of glass to your heating elementThe quality of heat distribution within the kilnThe circulation of the air in the kiln chamberPreviously fired glass and whether it was a tack fuse or a full fuse
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
When initially heating the glass a suggested table for the various glass thickness:1/8“ thick – 600 degrees Fahrenheit per hour3/16” thick – 525 degrees Fahrenheit per hour1/4” thick – 250 – 450 degrees Fahrenheit per hour3/8” thick – 250 – 375 degrees Fahrenheit per hourCasting work – 120 degrees Fahrenheit per hour
Your firing schedule should include the following:Thickness of glassHeating rate (degrees per hour)Rapid Heating RateSoak Time at full fuseCooling RateAnnealing schedule
Do not look at your glass until it is above the
. 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. Room temperature to 1000 degrees FahrenheitSoak at 1000 degrees Fahrenheit for 15 minutes Raise temperature until it reaches about 1320 degrees Fahrenheit Soak for 10 minutes or until you have reached your desired lookShut door and cool down to 960 degrees FahrenheitSoak at 960 degrees Fahrenheit - 1 hour Lower temperature to 600 degrees Fahrenheit Turn off kiln until it reaches room temperature
Full Fuse – The glass layers melt into each other until they are flush. Room temperature to 1000 degrees FahrenheitSoak at 1000 degrees Fahrenheit for 15 minutes Raise temperature until it reaches about 1425 degrees FahrenheitSoak for 12 minutes or until you have reached your desired lookShut door and cool down to 960 degrees FahrenheitSoak at 960 degrees Fahrenheit – 1 hour Lower temperature to 600 degrees Fahrenheit Turn off kiln until it reaches room temperature
Slump - Bending glass into or over a moldRoom temperature to 1000 degrees FahrenheitSoak at 1000 degrees Fahrenheit for 15 minutes Raise temperature until it reaches about 1350 degrees FahrenheitSoak for 15 minutes or until you have reached your desired lookShut door and cool down to 960 degrees Fahrenheit - 1 hourSoak at 960 degrees Fahrenheit Lower temperature to 600 degrees Fahrenheit Turn off kiln until it reaches room temperature
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.
To keep track of your firing schedule record all of your projects in a glass fusing journal. Either print out a
, or you can purchase a booklet to keep all of your records in one place.
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