"C10RPL" Firing Schedule

Plainsman Cone 10R Firing

Every gas kiln is different so this schedule may not work for you if your kiln does not cool at the same rate or maintain the same atmosphere. Our kiln is brick construction, downdraft, four natural gas burners, about 30 cubic feet. It fires evenly top-to-bottom and front-to-back. We have had and used others but none of them have equaled the quality of firing this can produce. It was built by Luke Lindoe around 1970.

It can rise while reducing so we do not do a separate body and glaze reduction (with an oxidation climb between). Reduction can be kept consistent throughout the kiln, enough to produce a clear bluish flame at the peepholes (with some yellow at the damper). We oxidize for half an hour at the end, turning the gas down enough to allow it to drop about 100F during that time. On shutdown, we seal it up but the temperature still free falls (although slower than a fibre kiln would). We open it at about 200F two days later.

Step	°C	°F	Hold	Time
1	10°C/hr to 120C	18°F/hr to 248F	0	12:23	Heat up overnight on pilots
2	50°C/hr to 550C	90°F/hr to 1022F	0	20:59
3	100°C/hr to 980C	180°F/hr to 1796F	0	25:17
4	50°C/hr to 1300C	90°F/hr to 2372F	0	31:41	Start light reduction beginning of this step
5	0°C/hr to 1280C	0°F/hr to 2336F	30min	31:41	Oxidation this step
6	0°C/hr to 30C	0°F/hr to 86F		31:41

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

How many degrees between these cone positions?

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!

Gas kiln near cone 10R in the Plainsman Clays studio

It is old, but nothing we have ever used fires as evenly and reliably as this downdraft kiln. It was built by Luke Lindoe in the 1960s. I have used it through my entire life as a potter since the early 1970s. Two burners at 2 inches oil-column will take it to 1000F fairly quickly, but it takes 4 burners at 4 inches and 20 hours to get it to cone 10. I can judge the back pressure and degree of reduction by the length and color of the flames at the peepholes and color of the flame passing the damper at the back. Changing the damper position by an eighth of an inch during reduction is enough to discern a change in the flame.

Cone 10R load of fired ware in Plainsman gas kiln

It fires evenly in temperature and atmosphere from top to bottom, front to back. Nothing more can be expected for any studio kiln. We use the C10RPL firing schedule.

Another view of the gas kiln in the Plainsman clay studio

Example of a modern automatic firing reduction gas kiln for use by studio potters

Courtesy of Bailey Kilns.

Sculpture Clay in functional ware? Yes!

This is Plainsman Sculpture-clay. At cone 10R it is vitreous, a deep brown low porosity body. The particles of grog create a beautiful surface. The glaze is G2571A bamboo matte. It was fired using the C10RPL schedule. By Tony Hansen.

Links

Recipes	GR10-A - Pure Ravenscrag Slip Ravenscrag all by itself makes a great cone 10 reduction semi-gloss glaze. It also has great working properties.
Recipes	L3341B - Alberta Slip Iron Crystal Cone 10R By adding a little iron to 100% Alberta Slip you can make an iron crystal glaze.
Recipes	GA10-B - Alberta Slip Tenmoku Cone 10R You can make a tenmoku from Alberta Slip by adding only 2% iron oxide and 5% calcium carbonate
Recipes	G2571A - Cone 10 Silky Dolomite Matte glaze A cone 10R dolomite matte having a pleasant silky surface, it does not cutlery mark, stain or craze on common bodies
Recipes	G1947U - Cone 10 Glossy transparent glaze Reliable widely used glaze for cone 10 porcelains and whitewares. The original recipe was developed from a glaze used for porcelain insulators.
Recipes	GR10-B - Ravenscrag Cone 10R Gloss Base Cone 10 Reduction glaze made using 90% Ravenscrag Slip.
Recipes	GA10-D - Alberta Slip Black Cone 10R You can make a black glaze at cone 10R using only 1% black stain in a 100% calcine:raw mix of Alberta Slip
Firing Schedules	Plainsman Electric Bisque Firing Schedule Three-step to 1832F
Typecodes	Reduction Firing

By Tony Hansen
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