We use this schedule to fire clay test bars. Pieces in the kiln have not been bisque fired and are generally not glazed. All the other temperatures (from 06 to 10) follow that same pattern, slowing down for the last 100 degrees F to top temperature and then holding for 10 minutes. If the kiln is more densely packed we lengthen the first step hold time (to drive out all residual water from body and glaze) and hold for longer than 10 minutes. This rate of increase is one that our kilns can manage, even when their elements age.
For glazed ware, it is essential to do a drop-and-hold and optionally, a slow cool firing, such as C6DHSC or PLC6DS.
We always include a self supporting cone. If the cone does not fall the correct amount, we adjust the firing schedule for next time.
Step | °C | °F | Hold | Time | |
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1 | 55°C/hr to 121C | 100°F/hr to 250F | 60min | 2:45 | |
2 | 194°C/hr to 1148C | 350°F/hr to 2100F | 0 | 8:02 | |
3 | 60°C/hr to 1204C | 108°F/hr to 2200F | 10min | 9:07 |
I document programs in my account at insight-live.com, then print them out and enter them into the controller. This controller can hold six, it calls them Users. The one I last edited is the one that runs when I press "Start". When I press the "Enter Program" button it asks which User: I key in "2" (for my cone 6 lab tests). It asks how many segments: I press Enter to accept the 3 (remember, I am editing the program). After that it asks questions about each step (rows 2, 3, 4): the Ramp "rA" (degrees F/hr), the Temperature to go to (°F) to and the Hold time in minutes (HLdx). In this program I am heating at 300F/hr to 240F and holding 60 minutes, then 400/hr to 2095 and holding zero minutes, then at 108/hr to 2195 and holding 10 minutes. The last step is to set a temperature where an alarm should start sounding (I set 9999 so it will never sound). When complete it reads "Idle". Then I press the "Start" button to begin. If I want to change it I press the "Stop" button. Those ten other buttons? Don't use them, automatic firing is not accurate. One more thing: If it is not responding to "Enter Program" press the Stop button first.
Here is an example of our lab firing schedule for cone 10 oxidation (which the cone-fire mode does not do correctly). To actually go to cone 10 we need to manually create a program that fires higher than the built in cone-fire one. Determining how high to go is a matter repeated firings verified using a self supporting cone (regular cones are not accurate). In our lab we keep notes in the schedule record in our account at insight-live.com. And we have a chart on the wall showing the latest temperature for each of the cones we fire to. What about cone 6? Controllers fire it to 2235, we put down a cone at 2200!
Four o'clock. These are self-supporting cones, use these. I was consistently getting the cone on the left using a custom-programmed firing schedule to 2204F (for cone 6 with ten minute hold). However Orton recommends that the tip of the self supporting cone should be even with the top of the base, not the bottom. So I adjusted the program to finish at 2200F and got the cone on the right. But note: This applies to that kiln with that pyrometer, our other test kiln puts cone 6 at 4 o'clock at 2195F. Of course, if you want the kiln to hold at cone 6 for longer the cone will bend further, so the top temperature would need to be reduced to compensate for that. If you are using the automatic programs (e.g. cone 6 schedules go to around 2230!) your kiln is almost certainly over firing.
A batch of fired test bars that have just been boiled and weighed, from these we get dry shrinkage, fired shrinkage and porosity. Each pile is a different mix, fired to various temperatures. Test runs are on the left, production runs on the right. Each bar is stamped with an ID and specimen number (the different specimens are the different temperatures) and the measurements have all be entered into our group account at insight-live.com. Now I have to take each pile and assess the results to make decisions on what to do next (documenting these in insight-live).
These have already been measured to deduce drying shrinkage. After firing they will be measured again to calculate the firing shrinkage. Then they will be weighed, boiled in water and weighed again to determine the water absorption. Fired shrinkage and absorption are good indicators of body maturity.
Recipes |
GR6-H - Ravenscrag Cone 6 Oatmeal Matte
Plainsman Cone 6 Ravenscrag Slip glaze. See more at ravenscrag.com. |
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Recipes |
G1214M - Original Cone 6 Base Glossy Glaze
A recipe developed by Tony Hansen in the 1980s. Its was popular because of the simplicity of the recipe and how well it worked with chrome-tin stains. |
Recipes |
G1215U - Low Expansion Glossy Clear Cone 6
A recipe sourcing high MgO (from Ferro Frit 3249) to produce a low expansion glass resistant to crazing on lower silica porcelains. |
Recipes |
G2587 - Floating Blue Cone 5-6 Original Glaze Recipe
Floating Blue is a classic cone 6 pottery glaze recipe from David Shaner. Because of the high Gerstley Borate content it is troublesome, difficult. But there are alternatives. |
Recipes |
G1214W - Cone 6 Transparent Base
A cone 6 base clear glaze recipe developed by deriving a recipe from a formula taken as an average of limit formulas |
Recipes |
g2851H - Ravenscrag Cone 6 High Calcium Matte Blue
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com. |
Recipes |
GR6-C - Ravenscrag Cone 6 White Glossy
Plainsman Cone 6 Ravenscrag Slip based white glossy glaze. It can be found among others at http://ravenscrag.com. |
Recipes |
GR6-D - Ravenscrag Cone 6 Glossy Black
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Recipes |
GA6-G1 - Alberta Slip Lithium Brown Cone 6 Low Expansion
Plainsman Cone 6 Alberta Slip based glaze. It can be found among others at http://albertaslip.com. |
Recipes |
G2928C - Ravenscrag Silky Matte for Cone 6
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com. |
Recipes |
GA6-A - Alberta Slip Cone 6 Amber Base Glaze
An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares. |
Recipes |
GR6-E - Ravenscrag Cone 6 Raspberry Glossy
A chrome-tin burgundy glaze using the Ravenscrag cone 6 base recipe. |
Recipes |
GA6-G - Alberta Slip Lithium Brown Cone 6
Plainsman Cone 6 Alberta Slip based glaze. It can be found among others at http://albertaslip.com. |
Recipes |
GR6-A - Ravenscrag Cone 6 Clear Glossy Base
This Plainsman Cone 6 Ravenscrag Slip base is just the pure material with 20% added frit to make it melt to a glossy natural clear. |
Recipes |
G1214Z - Cone 6 Silky Matte
This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte. |
Recipes |
GR6-B - Ravenscrag Cone 6 Variegated Light Glossy Blue
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com. |
Typecodes |
Oxidation Firing
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Firing Schedules |
Plainsman Cone 6 Slow Cool (Reactive glazes)
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Firing Schedules |
Plainsman Electric Bisque Firing Schedule
Three-step to 1832F |