"C04PLTP" Firing Schedule

Plainsman Low Temperature Drop-and-hold

We use this schedule for cone 06, 05, 04 and 03, adjusting the top-temperature and hold-temperature as needed.

We never use the built-in programs on kiln controllers because this schedule gives better results. We seldom fire cone 06, glazes melt better at 05 and cone 04.

The drop-and-hold temperature if 100F below top. For example, if you are firing to cone 05, then top temp will be about 1860 and the drop-and-hold temp will be about 1760 (according to what your firing cone indicates).

The slower approach at the end is important to even out the kiln chamber, that is why a longer hold is not needed at top temperature. The drop-and-hold is important, this helps heal pinholes and blisters. The cool is freefall. Your rate-of-fall may be quite different than ours, depending on how well your kiln is insulated, how big it is and how heavily it is loaded.

Step	°C	°F	Hold	Time
1	55°C/hr to 121C	100°F/hr to 250F	60min	2:45	Water smoking step
2	194°C/hr to 1004C	350°F/hr to 1840F	0	7:17	As fast as your ware can tolerate
3	55°C/hr to 1060C	100°F/hr to 1940F	10min	8:27	Slow approach to top, hold longer for larger kilns (this is for a small test kiln)
4	500°C/hr to 1004C	900°F/hr to 1840F	30min	9:04	Drop 100F and hold
5	0°C/hr to 23C	0°F/hr to 75F		9:04

Start temperature assumed: 25°C or 75°F
"Fahrenheit degrees" is not the same as "degrees Fahrenheit". A 100° reading on a Fahrenheit thermometer is equal to a 37° reading on a Celcius thermometer. But "100 Fahrenheit degrees of temperature change" is equivalent "55 Celsius degrees of change". That is an important distinction to understand the above temperature conversions.

Related Information

Program your firings manually, calibrate the final temperature using cones

Tap picture for full size

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!

How many degrees between these cone positions?

Tap picture for full size

Two orton cones, one bent to 6 oclock, the other 4 oclock.

I was consistently getting the cone on the left when 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 (they consider the indicating part of the cone to be the part above the base). So I adjusted the program to finish at 2200F and got the cone on the right. But note: This applies to that kiln at that point in time (with that pyrometer and that firing schedule). Our other test kiln bends the cone to 5 o'clock at 2195F. Since kiln controllers fire cone 6 at 2230 (for the built-in one-button firings) your kiln is almost certainly over firing!

Links

Recipes	G2853B - Cone 04 Clear Ravenscrag School Glaze A Ravenscrag Slip base made by simply mixing it 50:50 with a frit
Firing Schedules	Plainsman Electric Bisque Firing Schedule Three-step to 1832F
Firing Schedules	Bartlett Fast Bisque Cone 04 120F/hr to 250F, 300/hr to 1000, 150/hr to 1100, 180/hr to 1695, 108/hr to 1945
Typecodes	Oxidation Firing

By Tony Hansen
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