Cones Or Rods For Kiln Sitter? Which Ones?

[TortoiseAvenger]

Just got a kiln, wondering what cones to get. The clay I bought can be fired anywhere from cone 6-10, and all of my glazes I'm considering are either 6 or "5-6". I was thinking I'd purchase cones/rods in 6, 8, and 10... but I read somewhere that using a cone that is one number higher than what you want is advisable. What do you think about this?

 

Also, I'm not sure whether to get the cones or the rods. Any opinions?

 

Thanks!

 

TA

[dhPotter]

If you have a kiln sitter then use bars in it.  If you are firing Glaze to cone 6 then get cones in 5, 6, and 7 and bar cone for ^6.  Be sure to get the self supporting cones.

 

Go here for cones. Page down to the bottom. Just get a box of each.  Don't forget about cone bars for your bisque firing.  I bisque fire to cone 04.

 

http://www.baileypottery.com/cones/cones1.htm

 

Good Luck

[CarlCravens]

That depends on what cone you plan to fire to. 

 

Orton's web page has various downloadable booklets about cones.  Their "Cones & Firing" booklet is pretty comprehensive:

 

http://www.ortonceramic.com/resources/product/pyrometric-cones/

[Min]

 The clay I bought can be fired anywhere from cone 6-10, and all of my glazes I'm considering are either 6 or "5-6"

 

Are you making functional pots with this clay? A ^6 clay can't go to ^10 without bloating or warping and a ^10 clay will be underfired and porous at ^6. No worries if it's for sculpture but not advisable for functional pots.  A clay rated at ^6-10 might be okay at the higher temps but not at the lower. I would look into a clay rated as ^5 or ^6 if you are using glazes in that range.

 

As dhPotter said, since you are considering ^5-6 glazes then I would get 5, 6, and 7. For bisque I go to ^04 (for a ^6 or ^10 clay) For a sitter use bars, for witness cones use the full size regular or freestanding ones. (regular ones are cheaper and it only takes a few minutes to make the clay bases to place them in, just get the angle right). For the glaze firing I would use a ^6 bar but watch the witness cones.

[bciskepottery]

If I remember the photos of your kiln correctly, I think your kiln tops out at cone 8 -- I think the kiln plate said max temp was 2300F and it only pulled 30 amps. That rules out cone 10.

 

If you are planning to fire only to cone 6, then buy cone 6 clay, not a cone 6 to 10 clay body. At cone 6, that clay body will not vitrify, resulting in weeping/seeping vessels. An underfired clay body will absorb water and, if put in a microwave or over, will cause problems. And, you may have issues with cone 6 glazes not properly fitting a cone 6 to 10 clay body.

[Bob Coyle]

You need to zero in your kiln if you are using a kiln sitter. Put a cone 5 bar in the sitter. Put witness cones 5-6-7 in the kiln mid way up and  in front and at least an 2 inches away of a peep hole. set up a firing cycle recommended by the manufacturer. Then periodically check the cones through the peep hole. When  the middle cone 6 starts to bend almost half way, adjust the sitter so the shut off drops. This should give you a relatively reproducible ramp to cone 6 down. 

 

If the bar looks like it will drop the shutoff before cone 6 is down, then adjust the slider up. All of the kilns I ever owned required the next higher bar ( cone 7) in the sitter and took at least three runs with sitter adjustments to give me a ramp to shutoff that I could trust.  You need to ALWAYS track your ramp and be aware of what is going on in your kiln, even if you have an automatic programmer. Usually the last hour or so is the most critical if you are just using a kiln sitter and don't have a cooling cycle.

[TortoiseAvenger]

Thanks for all the responses! So much good advice... Keep it comin