Tuesday, September 22, 2009

Kiln Temperature Log 2

I think that the pyrometer is one of the best tools to help you fire your kiln. I usually log the temperatures by hand and then plot them on a grid chart with the log of gas, air and damper settings below that. (The first photo has the Hobo graph on top and my chart below.)

I log the temperature every hour or so depending on when I check it and just make sure it is going up in value.

But with this Hobo Data Logger you can have it record temperatures every minute, every 2 minutes, every 5 minutes, every hour, etc. and you don't have to be present. You just set it and go. You can have it wirelessly send it to your computer or just pick it up at then of the firing and print it.

So what that means is on this last firing I noticed the temperature rose in a looping pattern early. (A detail that was not present in the hand log because I did not have as many plot points.) This made me realize that I could probably be turning up my kiln about 15 minutes earlier to maximize the fuel usage.

That way I could keep the kiln temperature rising in a more straight line pattern.

Now I know that is not really necessary as the kiln bricks, posts, shelves and work are all absorbing heat and each has their own rate of absorbing that heat, so small adjustments may not translate to the same savings by the end of the firing, but it is a way that we can use the tools we have to try to improve our firings.

It is just another step from the first improvement where I realized that I did not need to leave the damper completely open during the early stages of the firing to insure oxidation but moved it to half open in hopes of keeping the heat in the kiln and heating the work instead of heating the air in Mitchell County, NC.

Then, the next improvement came after oxidizing a load of work. Afterwards I noticed my settings and realized that I could use this information to further improve my early settings.

Since I now knew that 2 1/2" open on the damper oxidized the kiln when it was at the firing peak, I deduced that 3" on the damper in the early stages would surely be oxidizing when the kiln was on low. So I made my early setting 3" and 3 turns on the primary air.

That improvement alone saved me about 3 hours off the firing time!
Another thing the Hobo showed us was that every time we opened the spy to look at the cones and glazes the temperature dropped considerably! So perhaps not looking made the kiln go up faster. (The watched pot...)

One application of these Hobo devices is to record weather related information where the worker doesn't need to be present, like in the Arctic. They can record air temperatures all winter long, several times a day, and send that info back to scientists in their labs. Or the scientists can pick up the device in the summer and then have the data they need.
Just thought you might like to know about this,

John Britt


Clay Club said...

Man are you a nerd ;)

John Britt said...

Did you say Turd?

Clay Club said...

that too

carter gillies said...

I am curious if you were getting back pressure out the spies when you noticed the temp drop. It might be overly obsessive, but if the temp fell because of cold air getting sucked in I suppose you could fiddle with the damper some and then reset it after the spy was closed. Do you see anything for or against this?

John Britt said...


I am sure it is back pressure when the kiln is in reduction and air coming in when it is oxidizing.

I was just showing how the pyrometer that was reading twice a minute would show those flucculations.

I know some people who use this concept to help even out kilns. They open the top spy and try to make the kiln act more like an updraft.

Anyway thanks for the ideas.

Nora Thomas said...

one more step to understanding what the frijoles is going on in that kiln! interesting. . .

carter gillies said...

Hey John,

Thanks for answering my comment/question. I guess my next question is whether there is temp loss during BOTH the reduction and oxidation phases when the spy is unplugged. Is the loss even enough to worry about controlling? If it is much greater during the oxidation would it make any sense to slightly damper the kiln while you check cones? I suppose some kilns can get back pressure with a neutral atmosphere or only mild reduction. Of course this might make it more difficult to read the cones, but I guess I am wondering if you can limit the temp loss. Just curious. This temperature graph seems like an ideal opportunity to explore just how much control you can exert in firing. Thanks again for the response.

John Britt said...


You are right to think about the implications. I did not try it during reduction but would assume the the temperature would rise do to the increase air and the excess fuel.

I did not try to control it but know that sometimes we like to check the kiln a lot and that may be counter productive...but not always,

Scott said...
This comment has been removed by the author.
Scott said...

Cool (hot) application, thanks for the post and the mention of the HOBOs!

Lisa researching ceramics said...

That's really neat! I never thought of making chart to record this. Thanks for sharing! I love your blog posts.