bottom shelf after firing
First of all I want to thank everyone who gave me support on my blog and by email while I was firing my kiln. All of your advice is so helpful and I truly appreciate each and everyone who gives advice. If you are a reader of my blog and have never commented, please don't be shy, just chime in with any and all advice or comments. I learn something from everyone who comments here, and I also learn something from every blog I read and comment on. Be sure to read the next to the last paragraph of this post to read an example of one thing I learned from another blog.
my Skutt kiln
After I posted about being scared to fire my kiln for the first time, I was feeling kind of sheepish. I almost deleted the post. But then I thought, no, someone else may be feeling the same as I did, afraid to fire their kiln and my post may help them in some way. I think my fear stemmed from the fact there is electricity involved. To me fire isn't so scary, electricity is. I also had a bit of a fear of failure, of having a problem with the kiln I couldn't solve or not knowing what to do. I was also worried because I purchased the kiln used and I was hoping I didn't buy a lemon or something. Well all that's behind me and I can now say I highly recommend facing your fears.
middle shelf after firing
I have a Skutt Model 181 which was new in 1988, so it's 21 years old. It has a 22" x 17" heating area and has a sitter, which means it is manually operated but will turn off automatically by the sitter. The woman I purchased it from previously used it to fire porcelain china dolls and it is in very good condition. It came with shelves and posts and some supplies. I purchased a pyrometer and installed it so I would know the temperature inside the kiln as the firing progresses.
cones on bottom shelf after firing
I made up a set of 30 test tiles for three Cone 5/6 clays I purchased from Aardvark Clay in Los Angeles. The clays are Nara 5, a mid fire porcelain good for throwing which fires very white, SRFG, a stoneware red with grog, and Cassius Basaltic which fires an ebony black. I pressed a texture on the tiles and hand formed them into an L shape. Each test tile has a scribed number on the back. For this firing I put three test tiles of each clay on three shelves in the kiln, bottom, middle and top. I also put a set of four pyrometric cones on each shelf, 07, 06, 05, 04. I put a sitter cone 06 in the sitter. I was planning on firing my bisque to 06. What cone do you fire your bisque to? I have heard that many potters fire their bisque to 04 and I am curious why or which cone is better to fire to? I made my test tiles quite some time ago, so I know they are good and dry.
my pyrometer during firing
I pushed the pyrometer into the kiln to the prescribed distance. As the Skutt manual recommended, I put in three spy hole plugs, but left the top one open. I propped the lid open with a stilt and turned the kiln on to low. Previously I had typed up a firing log which is just a grid with a spot for the date, time, temperature, and notes. I kept the firing log close by to observe the firing and document it on the firing log. I can't emphasize enough about using a firing log. I have a good memory, but the documentation is a wealth of information which can be referred to once the firing is complete, especially for a manual kiln, a new kiln, or for a person new to firing. Another use for a firing log is making comparisons to previous firings. When the kiln starts to take longer to fire, this may mean you need new elements or some other type of kiln repair.
cones on middle shelf after firing
I read that the 200 F and 600 F temperatures are critical points in firing. At 212 F water starts to boil, any water left in the clay may boil and cause the clay to explode or crack, so firing slow up to and during that time is important. The idea is to burn off the moisture in the clay but slowly so it doesn't pop, crack or explode. Certain chemicals in clay including chemical water start to burn out from 530 up to 900 F, so this is another critical point in firing and another time to fire slowly to give the clay time to equalize and stabilize. I am presuming the same will be true for a glaze firing as the clay will absorb moisture from the glaze and there are chemicals in the glaze too.
cones on top shelf after firing
According to my log here is how the firing progressed. I began firing at 12:30 p.m. by turning the kiln to low. It took just one hour for my kiln to reach 250 F on low - way too fast. It took another two hours for the kiln to reach 500 F. At 3:00 p.m. I turned the kiln to medium. By 4:00 p.m. the kiln had reached 650 F, too fast again. The Skutt manual recommended leaving the kiln on medium for one hour and then turning up to high. I turned the kiln on high at 4:00 p.m. At 6:10 p.m. the kiln reached approximately 1790 and the kiln shut off automatically. At 6:30 p.m. the temperature had dropped to 1650 F; at 8:30 p.m. the kiln had dropped to 1000 F; at 10:30 the kiln was 550 F. The next morning the kiln read 150 F at 6:00 am. The top spy hole was left out during the whole firing.
cone in sitter after firing
Cone 07 and 06 melted on the bottom and middle shelf. On the top shelf cone 07's top blew off and I am not sure where it went and none of the cones melted. But to be fair the top shelf was very close to the top and the top spy hole was open with the cones directly in front of the hole, next time I need to put the top shelf cones in the back of the kiln on the top shelf. When I examined the top shelf cones 07 and 06 they are both shiny or glassy, see the next to last paragraph for more information about this observation. Oh, I just noticed the top kiln shelf doesn't have any kiln wash on it. I have a lot to learn.
I would like to slow the kiln down at the beginning. I plan to prop the lid up a little higher and to remove one more spy hole. Or perhaps I can just turn the upper control on low and leave the lower one off. What do you think? I will attempt to leave the kiln on low till I pass the 600 F temperature. What do you think about that? I will repeat this bisque firing with the adjustments noted above. I can use the same test tiles and I can replace the Cone 07 and 06 cones and re-use the Cone 05 and 04 cones. What do you think, maybe I shouldn't reuse the cones? If you have ANY comments, recommendations or corrections to my observations, please don't hesitate to let me know, I gladly welcome your thoughts and advice.
Oh, one more thing, remember at the beginning of this post I said I learn something from every blog I read and comment on. Well a short time ago, I asked Kitty of Kitty's Spanish Studio on her blog, how she could tell a clay was vitrified. She said she could often tell a clay was vitrified by the glassiness of the clay. I wondered about that and put that thought in the back of my mind. When I was looking at the cones that melted during the firing, guess what? The melted cones had a different sheen, they were shiny. I'm finding out ceramics is about testing, observation, and record keeping. Really ceramics is a science and an art.
The dahlia above is from my garden and is seven inches across, unbelievable. And today is my 24th wedding anniversary, unbelievable how quickly time flies. And...some ravens are flying in next, so stay tuned.