First Gas Kiln Firing
There are several firing methods in ceramics: electric, gas, vapor, pit, wood, and a few others. In the very recent past, I’ve fired in an electric kiln because this is the equipment that I own and operate in my home studio. I have had my work fired in a gas kiln while I was in college, but never actually operated the kiln myself. Last weekend, I had the opportunity to participate in a gas kiln firing at the Colorado Potter’s Guild where I am a new member. The guild acquired a new 25 cu. ft. Cooperworks gas car kiln last summer and many of the members are hesitant to fire it. Let’s face it, we’re all creatures of habit - myself included.
I showed up for the workshop because I want to be able to learn how to fire it myself without having to depend on others to fire my work for me - though I’ll be hard pressed to fill a 25 cu’ kiln myself at the rate I produce work. If the firing isn’t quite as expected, I will have no one to blame but myself. Not knowing a ton about gas firing, I’ve decided to learn all I can about this method of firing. Yep - the same geek who was hell bent on hosting my own blog and setting up my own website also wants to KNOW how to use the gas kiln successfully.
For those of you who are not ceramic people, gas firing is desirable because you can get different effects from a reduction environment. When I say reduction - I’m referring to an atmosphere that is deprived of oxygen (though gas kilns can also be fired in oxidation). Electric kilns have an oxygen atmosphere, hence the term “firing in oxidation”. What does this mean? Each firing method produces different results. For example copper can turn red in a gas firing - whereas, it will turn green in an electric kiln.
This past weekend, we fired the “Coop” to ^10 and experimented with different reduction times and temperatures. For those of you unfamiliar with the symbol ^ or the term cones - it refers to the temperature to which the kiln is fired. ^10 is approximately 2340° F. Want to see the cone chart? Click here. When I fire my electric kiln, I fire to ^6 or approximately 2232° F. 100+ ° F doesn’t seem like a lot, but it affects how a glaze melts - so when ceramic people are searching for glaze recipes, they’re also looking at the ^ of a recipe in order to achieve successful results. Firing at a lower temperature is also more economical. On a side note, potters are taking note of our consumption of natural resources - there are groups who are firing their kilns using geo-thermal energy and I am eventually going to try going solar for my electric kiln in my own studio.
So what am I currently reading? The Complete Guide to High-Fire Glazes by John Britt and a classic, Kilns: Design, Construction, and Operation by Daniel Rhodes.
I only added 3 pots to the guild firing and was rather unimpressed with the results. Not being familiar with the guild’s glazes, I used my usual application method and dipping time. Turns out, I need to dip the pots longer than my usual 3 second dip time according to one of the other members - my application was too thin. Now I know - but will share my results nonetheless:
The first 2 images are the same bowl - glazed with a tenmoku glaze. The 3rd and 4th images are the same bowl - glazed with ohata khaki (a gorgeous iron red). The interior is beautiful - but the exterior crawled terribly. I washed my original glaze choice off the bowl the same day as the firing and didn’t allow enough time to dry completely before glazing again. The 5th image is a celadon, which should be more green/blue. The bowl had too thin of an application of glaze and the result is a pale olive green glaze. It also had some kiln shelf debris that fell into it. Good thing the glaze turned out so poorly.
Even mistakes are good learning opportunities. I signed up to fire the kiln in late April with 2 other potters, so hopefully, I’ll have a little more success the next time. In the meantime, it’s a beautiful day - so I’m heading out to the studio as soon as I’ve signed off.
Have a great weekend,
~Cynthia
