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#1 MellissaB

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Posted 05 November 2012 - 04:40 AM

Hello

I am looking for some clarification regarding the different firing temperatures for Orton cones. I have an old Harrison Mayer kiln, which uses a kiln sitter, and so make use of the small cones. I recently noticed in the Hamer's 'Potters Dictionary' that the firing temperatures for the cons are not the same. It seems to me that there is quite a large difference, for example the large cone 04 has a temperature of 1060 degrees C (when heated at 150 dC), while the small cone 04 has a a temp of 1098 dC (when heated at 300 dC - almost 40 dC).

If I fire an earthenware glaze, which matures between 1060 - 1120, which cone would I put in the kiln sitter - the small 02 or is it safer to use a lesser 03? According to Hamer, the large Cone 02 is 1120, small cone 02 is 1150, but my local potters supply shop sells both the large and small Orton cone 02 as 1120 dC.

I have an almost new box of small cone 02's, which is why, if it makes no difference, I'd prefer to use them.

Hope that someone can advise,

Thanks,
Mellissa Bushby.

#2 Marcia Selsor

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Posted 05 November 2012 - 07:32 AM

Your kiln setter is made for small cones. This has all been worked out b the industry. Use the small cone if that is what your glazes are rated for. You could try an 02, but I would test it first with your glazes. The difference between 04 and 02 in Fahrenheit is almost 100 degrees.It could make glazes run. If you use the 02 in a firing , you could also use a cone pack for witness cones and watch as they melt. The cones reflect a truer reading of what the ceramic material is doing more so than a pyrometer. It is the heat work that is the significant factor that cones reflect.

Marcia



#3 JBaymore

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Posted 05 November 2012 - 10:57 AM

The small cones when placed in a kiln sitter act pretty much like the large cones when placed on a shelf. The weight of the top bar of the sitter, when placed in the middle of the small cone, causes it to "kill" the sitter at approximately the same time as a large cone of the large series would have the tip equal to the base (be "down"). So a 04 small cone in the sitter is about the same as a large 04 sitting on the shelf supported at the proper angle.

Of course the exact placement in the sitter of the small cone can have a dramatic impact on the melting, bue to the variations in the placement of the sitter's bar weight.

So test, test, test.


best,

......................john
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#4 Pres

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Posted 05 November 2012 - 11:18 AM

Hello

I am looking for some clarification regarding the different firing temperatures for Orton cones. I have an old Harrison Mayer kiln, which uses a kiln sitter, and so make use of the small cones. I recently noticed in the Hamer's 'Potters Dictionary' that the firing temperatures for the cons are not the same. It seems to me that there is quite a large difference, for example the large cone 04 has a temperature of 1060 degrees C (when heated at 150 dC), while the small cone 04 has a a temp of 1098 dC (when heated at 300 dC - almost 40 dC).

If I fire an earthenware glaze, which matures between 1060 - 1120, which cone would I put in the kiln sitter - the small 02 or is it safer to use a lesser 03? According to Hamer, the large Cone 02 is 1120, small cone 02 is 1150, but my local potters supply shop sells both the large and small Orton cone 02 as 1120 dC.

I have an almost new box of small cone 02's, which is why, if it makes no difference, I'd prefer to use them.

Hope that someone can advise,

Thanks,
Mellissa Bushby.


Another variable when using the small cones in a setter is the position of the cone in the holder. Placing the cone directly in the center so that the center rod comes in the middle of the cone gives you the closest approximation of heat work at your cone number. However, if you place the cone so that the rod is more to the thicker part of the cone, or the thinner part you get a little variation in the kiln work, sometimes as much as +-50% in the cone number. I used to use this characteristic to fire some loads a little bit hotter because the glazes got a little richer in texture this way. Now days, I use the Pyrometric bars instead, as these are consistent in thickness thus having now variation in temp no matter how they are place-so long as secure.

Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/





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