Post #782192 by MadDogMike on Mon, Dec 11, 2017 9:41 AM

Thanks guys, I'm going to try that Krakatoa mug at least one more time and try to "perfect" it.

Here's little useless kiln geek information that someone may find interesting. Kilns fire to a "cone number". Starting with Cone 022 (also designated ^022) as the coolest and going up through ^14 as the hottest. ^04 is hotter than ^06, and ^4 is hotter than ^04. There is no ^0, the next step from ^01 is ^1. (...:down:, 03, 02, 01, 1, 2, 3, :up: ...). Lusters like real gold trim fire fairly cool (1000 degrees) at about ^018, low fire glazes are usually ^06, low fire bisque usually ^04, mid-fire clays about ^4-7, and high fire clays and porcelains at ^10-14. There is a temperature range for each cone but it also depends on the speed that it reached the temperature. The gold standard that has been used for 100 years is Orton Cones, a composite material that melts and bends over when the right time/temperature combination has been reached. You can see the 5th cone has over-fired (gotten too hot), the 4rd is fired just right so that the tip is just touching the floor, 1-3 have not gotten hot enough.

And why do I care? :lol: As many of you know, I am a hobby ceramicist. I make mostly to give away and don't really sell anything so ceramics are an expense for me, not a source of income (just a fact, not a complaint). So instead of a fancy, big, new-fangled kiln, I have an little old busted up one that works just fine for me :D My kiln originally had a Kiln-Setter that would turn the kiln off when it reached proper temperature but it stopped working long ago (I have the parts to fix it, just never got around to it). So now I use a pyrometer (hi temp thermometer) to tell when to turn off the kiln. But last few firings it seems like the temp was hotter than the pyrometer was reading so I decided to do an experiment. I put 4 cones in the kiln - 06, 05, 04, and 03. (Don't look at my filthy kiln, it needs to be vacuumed :o )

I fired the kiln yesterday to 1760 degrees on my pyrometer which should have been about ^07, here's the results I got.

The 06 cone over fired, it should have bent at about 1830 degrees. The 05 cone fired just about right, it is designed to bend at about 1890 degrees. The 04 cone (1950 degrees) was just starting to bend and the 03 cone (1990 degress) has not yet started. Based on these cones, my kiln fired to about 1890 degress and my pyrometer read 1760, looks like my pyrometer is reading about 130 degrees too low. I can either try to calibrate my pyrometer, add 130 degrees to the reading, or fix my Kiln-Setter. Why does it matter? Most low fire glazes fire to ^06 but some of the colors are susceptible to overfiring, the color will wash out and may even turn to a clear glaze. On the more extreme side, it can get hot enough to actually melt the clay into a puddle on the floor of the kiln!!! I just wanted to be sure I get it right before I fire the snake hut :)