What is the Correct Firing Temperature?

This is a question that I am often asked. The answer is that there is no absolute correct temperature. It depends on too many variables.

Some of these variables are: the type of kiln (brick or muffle), the location of the door and the heating elements, the size of the kiln, the age of the kiln, the carbon you use, the amount of carbon you use, the number of times you have used it, the box you fire in (steel, fiber blanket, ceramic, ceramic cloth, lava cloth, fiberglass cloth, etc.), the number of times you have fired in the same box, and finally, the altitude.

There is a simple way to figure out the right firing temperature for your kiln, which is trial and error.

Use bronze clay to make some test pieces, 3, 6, and 16 cards thick. If you have a muffle front loader kiln, fire them at 1550°F/843°C. If you have a brick kiln, fire at 1470°F/799°C. You can refer to my instruction manual for other conditions, such as box, carbon, and length of firing.

Take note of the firing conditions in which you did your test: carbon, box, etc.

After firing check the pieces. If they look curved, blistered, swollen, or somewhat textured, it means that this temperature is too high. Lower the temperature by 20°F (10°C) and repeat the test. Continue testing until you get smooth, strong test pieces.

To check sintering, use slight pressure to try to bend the thinner piece with your fingers. If it breaks, it means the temperature was too low. Raise the temperature by 20°F (10°C) and repeat the test.

A thicker piece may not break easily, even if it is not fully sintered. To check thicker pieces, sand the surface with course sandpaper. If the piece is not sintered, you will immediately see a non-metallic mass under the surface. Again, raise the temperature by 20°F (10°C) and repeat the firing until you get a strong, fully sintered piece.

Once you have found the correct temperature, try as much as possible to stick to the firing conditions you noted prior to your testing.

Next, look at the different schedules for the other clays, and adjust them accordingly. Now you have a customized firing schedule for your kiln.

Conditions may change, of course, so it is a good idea to test sintering after every firing. Buff or sand a hidden spot of the fired piece to see if there is non-metallic matter under the surface. If there is, you haven’t lost the piece. Just re-fire, or repair and re-fire.

I have just come back from teaching a workshop in Grand Junction, Colorado. It’s high desert, 4,700 feet above sea level. Two things happened that I had never encountered before.

First, the same candle warmers that I use in my studio (at sea level) were a lot hotter. They melted plastic, while at sea level I can dry a piece with a straw in it with no problem. Also, some of the kilns were firing too hot.

This seems somehow counter-intuitive, since from what I understand, because of lower air pressure, the higher the altitude, the longer it takes to heat; cooking rice takes longer, and baking bread requires adding dry ingredients.

Since this question may be relevant to metal clay users who live in high altitudes, I would appreciate any input on the subject that I can post on this blog.

The other thing that happened, was that Baldwin’s patina darkened the copper a lot more than I am used to seeing. This may be related to the composition of the air at higher altitudes, so again, if you happen to know the reason, I would love to hear it and let other people know.


10 Responses to “What is the Correct Firing Temperature?”

  • Kenji Says:

    Hello Hadar,

    Thanks for this update. I’ve printed it out and it now has a home just above my kiln as a reminder. Hope to see you this year Hadar…

  • Kim Shaffer Says:

    Thank you Hadar. I am in Monument, Colorado which is 6800 feet above sea level. My brick kiln has been frustrating to me and I was wondering if it had something to do with altitude also. It isn’t working now unfortunately but I have been using my muffle kiln instead. It seems to do so much better when firing copper and bronze at your temps on your latest blog for firing your quick fire clay. I do think that cooling is important. I found that doing the bronze and copper in the brick kiln was harder to do the cooling period. The muffle kiln I could just let it cool down on its own. The test samples from the muffle kiln that I did the last couple days have been very good. The tests from the brick kiln were fine for bronze but very odd for copper, it seemed sintered but was very brittle. Since my brick kiln is not working, maybe I was not getting the right temps that it was reading. I won’t know for sure until I get it squared away again. I do know that oven cooking in my altitude should be set about 5 degrees or so more than sea level.

  • Peggy Houchin Says:

    Hi Hadar, I live at about 5,000 feet in Loveland, CO. I’ve fired your Quick Fire Copper clay in my kiln at home using a fiber box with about 1/2 inch of carbon on bottom and top of the pieces. I’ve fired about 6-8 small to regular size pieces to 1530 degrees in a front loader kiln and had very nice results. No warping, breaking, etc. I’m still testing so I’ll post results. Thanks for all you do for us!

  • Jocelyn Cooley Says:

    Hi Hadar, I live at 4500 feet in Sedona, AZ. I’ve used your instructions for firing your copper and bronze. Works fine. Only had one piece not sinter thoroughly, but it was quite thick.
    Jocelyn

  • Lin Altman Says:

    Do you rinse off the Balwin’s after you apply it?

  • Hadar Jacobson Says:

    Jocelyn,

    When you have thick pieces in your batch it always helps to hold up to one hour at 1100F before continuing to the final hold temperature. Holding at this temperature allows the binder to burn out completely.

  • Hadar Jacobson Says:

    Lin,

    I do. This stops the reaction and prevents the surface from becoming murky (or green).

  • T Says:

    Excuse me but I’m very new to all of this and need Help! I have an SC2 Front Loader. I tried to test fire pieces that were both 1 1/2″ long x 1 1/2″ wide one was 5 cards thick and the other 10 cards thick. I went by your “Quick Fire White Bronze Instructions” for large pieces-Ramp at 900 degrees/hr and held at 1250 degrees for 2 1/2 hrs. It also says that this schedule can be used for thin/small pieces. I fired with that exact schedule and my pieces melted.

    Then I noticed on her “Quick Fire Clay Intructions” it says for thin pieces Ramp at full speed/hold at 1280 for 1 1/2 hrs. For thick pieces Ramp at full speed/hold at 1280 for 2 hrs. Which one should I go by?

    And I read that we can reuse the carbon. What’s the best way to sift the ash out of the carbon or can you use the carbon with a little ash in it as long as the pieces are covered when firing? Also when the firing is finished am I supposed to take the the pieces out of the carbon to cool or just leave it in the kiln till all is cooled?

    So then I got a bit confused. Any suggestions for me with the size and thickness I’m trying to fire?

    My head drops every time it doesn’t work. I really appreciate your help!

  • Lynn Latta Says:

    The experiments continue. Bisque pot cracked firing Copper after six firing so back to the Fiber. I have a schedule that is working consistently. Bronze: Ramp 2 to 1550 hold 1 hour.
    Copper: Ramp 2 to 1770 hold 1 hour. (ramp 2 is 500 degrees per hour)
    You have been key in my work. I just received your various clays and first book, it has given me great inspiration. Thank you for sharing

  • Lynn Latta Says:

    That firing schedule is for the other clay not Hadar’s. It just showed up and I have to mix it.

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