Bisque firing quit at 1353 after 6 hours

[Bear Creek Studio llc]

I hope you can reassure me I am ok.  My old kiln quit after 6 hours at 1353 degrees for bisque set for 10 hr firing.  It’s a speckled brown stoneware clay.  It’s now very pink.  It does appear to be ceramic and some of the pieces ring when tapped.  
 

Should I refire and do I do a complete 10 hr firing or can I do like. Quick 4 or 7 hour.  I have an old Gare kiln using. Ramp master 2 controller.  It failed at the breaker which we think was old 

 

thanks for your help

[Bill Kielb]

1353 is cone 017 ish. I assume you were trying to go to cone 04. I would suggest refine to 04, hopefully you are using cones. Bisque firing removes organics and chemically combined water so how much time and how much time at temperature is the important part. I would troubleshoot the kiln, fix it then re-bisque to desired cone.

[Kelly in AK]

It’s below the lowest temperature I would consider bisque fired. It’ll be fragile. More absorbent, glaze will go on thicker than you're maybe accustomed to. Some people glaze greenware, it works. This seems beside the point. I don’t even know that you’re planning to glaze your work. 

Put a piece underwater overnight to see if it’s ceramic yet, shouldn’t be able to scratch it with your fingernail. It doesn’t matter if you fire 6 hours, 10 hours, or 50 hours, the clay has to get hot enough to change. If your kiln fails at bisque, how are you going to do a glaze firing?

I agree with @Bill Kielb, troubleshoot everything from the breaker to the kiln. Fix that before making any other plans. Get some cones if you don’t have any, don’t rely on the pyrometer alone. There are no ceramics without a kiln (or a very very hot fire).

You are ok, by the way. Things will work out. 

[Bill Kielb]

5 hours ago, Kelly in AK said:

Some people glaze greenware, it works

FYI - Quite often once fire folks will do a single firing at bisque speeds. In effect a bisque first to burnout everything then continue on to glaze temp, usually for tested clay and glaze products that work well this way without excessive glaze defects. If their clay is known clean or tested with a glaze known to work without issue then not so much at the reduced speed but the tested speed. I would not ignore the time at temperature unless verified ok through prior testing.

[Kelly in AK]

Amen to that!

[Bear Creek Studio llc]

Thanks for all the comments I will refire to come 04.  We fixed the breaker which was old.  Thanks again for your help,  

[Bill Kielb]

11 hours ago, Bear Creek Studio llc said:

.  We fixed the breaker which was old

Ya probably already know this but worth mentioning I think. Breakers fail because they are old but also because they overheat. Here in the US the breakers you buy should not exceed 80% of the rating stamped on the breaker.  For kilns which are considered continuous loads by code, per code they require a breaker at least 125% of the kiln full load and not more than 150%. 

For a kiln that draws 40 amps, minimum breaker size is 50 amps (40X 1.25), maximum breaker size is 60 amps (40X1.5). I mention because electricians often get this wrong. The rule is there to prevent the breaker from overheating and failing prematurely. Often this is not common knowledge so I think worth passing along since you just experienced a worn out breaker on this kiln.

Edited May 12 by Bill Kielb

[PeterH]

4 hours ago, Bill Kielb said:

Ya probably already know this but worth mentioning I think. Breakers fail because they are old but also because they overheat. Here in the US the breakers you buy should not exceed 80% of the rating stamped on the breaker.  For kilns which are considered continuous loads by code, per code they require a breaker at least 125% of the kiln full load and not more than 150%. 

For a kiln that draws 40 amps, minimum breaker size if 50 amps (40X 1.25), maximum breaker size is 60 amps (40X1.5). I mention because electricians often get this wrong. The rule is there to prevent the breaker from overheating and failing prematurely. Often this is not common knowledge so I think worth passing along since you just experienced a worn out breaker on this kiln.

... and presumably the "house" wiring needs to be rated for the new breaker size. Which might be an issue for some retro-fitters.

[Bear Creek Studio llc]

Thanks for the info on the breaker I will check with husband make sure he knows this before I try to run kiln again.  My newer kiln has never done this (so far) 

I am so glad I found this forum. And folks are willing to share their knowledge and time to submit it

[Denice]

Refiring is need,  speckle clay have a  lot of impurities that need to burn out,  I use several clay's that have a excess of impurities.  I fire a slow C04 to keep my glazes clean.   Denice

[Bear Creek Studio llc]

Excited that I retired this load and we changed the breaker and it worked. I do think after the advice I received here we are going to make some changes.  Thanks again everyone