Sunday, March 26, 2017

Keeping your eye on your kiln

 I had to work on Friday and that left Mark here for the cone 6 firing that I was working on. Most of the time we will program the kiln to come on in the wee hours of the morning. Then it is usually finished around lunch time.
This time I asked him to turn it on as I was leaving and make sure we vented the hot wax out of the kiln before dropping the lid. We use hot wax, or paraffin to coat the bottom of the pots before they are glazed. It keeps most of the glaze off the bottoms and what is left can be easily sponged off.

 Mark let the wax vent off by leaving the lid and peep holes open after that he closed the lid, closed the peep holes and let it fire. It was going along as it should until it hit 2183 degrees. Our computer program is set up to hit 2190, then cool to 2175ish and hold 15 minutes. He looked and it said, 2183, he went back and it said, 2183. Here is what we did not know, how long it was holding at 2183. He tried to call me at the school, but because I am all over the building I missed his called, he called again, he called again, and finally I heard my cell phone go off. Here is what is going on. My reaction was, shut it off. I knew the glazes would be matured, my hope was that they had not been sitting there at 2183 so long that the glazes had become runny enough to over fire or that we had over fire the clay body.
In the morning, I took a  quick look.
Then shut the lid.
Then I slowly let the kiln cool.
350.... I started opening the lid, 325, open more 300 degrees I opened the whole lid and let thing cool to around 200 degrees.
I did lose a few pieces, such as the one at the top of the post, and 2 more that were the same combination.
I lost a few pots to the clay sticking to the top shelf. That was more my own fault for using an older shelf and not applying a fresh coat of kiln wash.
But, all in all the black glaze, with the top glaze that we have been working to salvage for over a year, worked. It melted, stayed on the pots and over all we like the results. Here's what we think happened, the kiln stalled when one of the thermocouples failed.  We looked back to find out when we bought this kiln and turns out we bought it almost 8 years ago. So yep, time to do a little maintenance. After which another fire to see if we can replicate the results.
It could have been worse, so much worse, I feel very lucky.
Remember when you are firing that computers can fail, your eyes are the best source to see that your kiln has finished it's job.


Barbara Rogers said...

That's such a relief that no more damage happened. Whew, I know you depend upon your pottery...and kilns too! Hope it can easily be fixed and work hard for many more firings.

gz said...

Nice results..hope you can replicate that!

Anna said...

a potters nightmare... glad the result were no worse and the black and blue is great.

cookingwithgas said...

Thanks all, yep one of those nightmares you don't want. Makes you think about safety with kilns. At least it's a good reminder.

Lori Buff said...

It is a good thing Mark was watching the kiln. Even kiln sitters can fail. Glenn Dair from Callanwolde tells the story about doing a bisque firing that got up to about ^15. A pot had somehow jammed the sitter so it never shut the kiln off, the kiln was unattended so it just kept firing until he got there in the morning. I have one of the shelves, it makes a great form for anything that needs a good curve.

cookingwithgas said...

Lori! Great story. Yes, eyes front.

Michèle Hastings said...

I am sure you shared this story with your students. It's the perfect example of how a kiln should be fired... with someone watching it!

The first pot in your post has a beautiful drip. It looks like a keeper to me... unless it's one that stuck to the shelf!

cookingwithgas said...

The drips worked out well, the glaze under went dry and lost color. This one didn't make the firing. It might work at the regular fire. It could have been worse. I'm big on never leaving a kiln unattended.