Sunday, December 6, 2009

Cone 6 Glaze Firings

After switched from cone 9/10 reduction firing to cone 6 oxidation firing, I have spent a great deal of times to deal with glaze problems. Mostly, pin holes. Even though I am also a ceramic engineer, I don't have much experiences with cone 6 glazes. Moreover, I have no clue what exactly those clay manufacturers added in their clays.

For the most recent firing, I drilled 2 of 1/4" holes on kiln lid, reset thermocouple reading 25 degree lower than actual temperature in the kiln (Cone Offset), used preset Slow Glaze Firing program, then, held 25 minutes in the end of firing. The pin holes were mostly gone.

Cone offset 25 degree for my kiln is actually about cone 7. Wow, without cone offset, it must be............................. No wonder so many pin holes.

Thermocouple reads actual temperature in the kiln. However, glaze doesn't react to temperature alone. It reacts to both time and temperature during the firing. How can I forget all about this!!??

on the left: cone offset 10 degree; around cone 8
on the right: cone offset 25 degree; around cone 7
before cone offset: many pin holes, especialy on the back

after cone offset 25 degree: 99.9% of pin holes are gone


  1. I need to do the same thing with my pyrometer. My first ^10 with this kiln, I had cone 11 down and it was reading cone 10. I think my pinhole problems came from my bisque fire, so on to solve that mystery! I have had them at ^04 and ^10 now.

  2. Judging from all this information on pinholing I will probably have to get a kiln that goes to a higher temp for my firing and use the one I have just for bisque. thanks for the info.

  3. Hey there, i really love your work and you seem to really know what your talking about. What do you mean by cone offset? just firing at a slightly higher temp?


  4. Hi Alex, cone off set is a program to " fool" the kiln. You can lower or higher firing temperature by reprogram kiln controller. In my case, what my thermocouple read was actuarially 25 degrees lower than what it sensed inside of kiln chamber. Most kiln controllers have this function.