New Kiln Build - Taking Your Temperature

[krispee]

Hi
am having a new kiln built, putting together a list of essential items, including bricks, gas burner etc. just wondering about what i might use to 'take the temperature' of the kiln, a Pyrometer looks good but others seem to use Cones.
to be honest i don`t know a lot about Cones but is there much of a difference in how these things work and are either of these two items worth looking at or should i look at something else?
any ideas?
by the way i`m from the UK before you guys suggest something and i`m building on a budget.....
thanks

Kris

[The Forge]

The use of 'cones' is the original way of telling the kiln's internal temperature. The 'cones' are clay that is compounded to melt at certain temperatures. There are charts that tell you the temperature that each one melts or sags. The idea is to place three 'cones', in view from the view hole, next to each other in the kiln . The one in the center 'sags' at the temperature you need, one on the left is higher temp.and one on the right is lower temp. So, what you should have at the end is one still standing tall, one slightly bent and one completely sagged over. In my book, you should install a good pyrometer since that will give you a much more accurate temperature reading as the kiln heats and then put 'cones' into the kiln as a check that the proper temp has been reached. Actually, since I had the ceramics background, I got all the workers in the Tool Shop to put cones in our metal heat treating oven as a check. :D

[tonofelephant]

Krispee,

Have used both cones and a pyrometer. Prefer by a long shot a pyrommeter.

Cones are the traditional way of firing out a kiln. Seeing the cones in a kiln through a peephole is sometimes problematic. Cones sometime do not bend at the right tempeture if they are very old or have picked up moisture (have had both problems).

Pyrommeters are imho a much better way of firing. With a pyrommeter, you can know exactly what tempeture you are firing to. With cones the firing zone can vary by as much as 50 - 60 degrees.

Cones are cheaper, intially, but for a larger gas kiln you need to have cones in several different spot in the kiln since there will be hot and cold spots. Also how picky are the glazes that you will be using? Some glazes run off a pot if you fire over by 25 degrees.

Out of curiousity, what size gas kiln are you making?

Carl

[krispee]

thanks for the replies, Forge, and, Carl.....
i`m guessing that you actually built your Pyrometers into the kiln, permanently?
my kiln is going to be a steel plate shell with fire bricks inside, gas burner at the back low down and to the side so it can direct the heat underneath and around any sculpture, and the size [inside the bricks that is] is going to be approximately 700mm high, by 470mm wide, by 470mm deep.......i`ll have a peep hole in the front with a drop down so it can be closed off and a slot in the top to let air in with a slider so that can be closed as well....the burner will be held rigidly, i`ve seen other DIY kilns with the stone holding down a burner, which has horrified me to be honest......most of the burners seem to be situated just outside the kiln blowing hot air in, that would also bring in some air of course.....
it would be easy to put another hole in the side say for a pyrometer as the guy is going to be welding it in a couple of weeks.......i haven`t got enough money to buy more than one item so i would have to go for either or i`m afraid.....

i was planning to do some glazing as well as standard firing and was wondering if it was possible to Raku fire using a kiln as well......
also i have heard wildly differing accounts as to just how long it takes to fire something, some leave their sculpture/pot in the kiln for 15 hours, some for 3 days!
just how much gas is that going to take?

Kris

[tonofelephant]

size [inside the bricks that is] is going to be approximately 700mm high, by 470mm wide, by 470mm deep.......i`ll have a peep hole in the front with a drop down so it can be closed off and a slot in the top to let air in with a slider so that can be closed as well....the burner will be held rigidly, i`ve seen other DIY kilns with the stone holding down a burner, which has horrified me to be honest......most of the burners seem to be situated just outside the kiln blowing hot air in, that would also bring in some air of course.....
it would be easy to put another hole in the side say for a pyrometer as the guy is going to be welding it in a couple of weeks.......i haven`t got enough money to buy more than one item so i would have to go for either or i`m afraid.....

i was planning to do some glazing as well as standard firing and was wondering if it was possible to Raku fire using a kiln as well......
also i have heard wildly differing accounts as to just how long it takes to fire something, some leave their sculpture/pot in the kiln for 15 hours, some for 3 days!
just how much gas is that going to take?


Krispee, I may have a slightly different direction to go. You can get the same size kiln made by Scutt for about $1,400. I had a Skutt whose inside measurements were 27" (700mm) in a octogaon shape and was 30" (778mm) tall. It had a kiln sitter/timer that would turn off the kiln when either the timer went off or the cone in the kiln sitter bent. Great system. With the timer/kiln sitter the kiln could either be shut off when the right tempeture was reached or enough time had elapsed. Great failsafe device if you forget the kiln. I added a pyrometer to it and used the kiln and pyrometer it for 10 years. We slumped glass, fused glass, and fired bisque and glazed huge pots in it. It needed 220 volts ac at 50 amps. Ate some electricity but gave repeatable steady results.

With the electric kiln, it heats evenly, really has no cold spots, and when you get the kiln just fire it up and go.

Also am a little concerned that you want to make the entire outside skin steel. You would be better off with a steel skeleton and then stack the bricks within the skeleton.

On a different note, as to the raku kiln. All you really need is a gas burner and an insulated wire cage to go over it. Also some need some pot tongs and a steel trashcan. Nothing fancy. Would seriously suggest that you take a raku class to learn about it. When I was in school, the mark of a serious raku person would be no hair on the arms, slightly singed eyebrows and seriously smoky clothes. Raku is fun, dramatic, and produces great pots. You need some instruction to get it right. You can get seriously hurt with raku or for that matter a gas jet kiln.

[racine]

this is barely my region but have used them[for investment wax burn out] so a couple of notes might be worth exploring..
1 i hope u r on mains gas as bottle gas will freeze up after half an hour or so depending on temp and flow.
2 gas blowers can go out, they excel at doing this in the middle of the night and just leave u guessing in the morning, there is a safety system to reignite the gas in tandem with a thermocouple, might be worth looking into, it may cost a bit but will be well worth it. this system may well control the temp and stages.
heres where i cant help... thats all i know, never had to make one.

the image here is a burn out kiln in a bronze foundry, china. the little smoking 'house' in the background, its fumes rising towards the daylight in the roof. what is interesting is that they build it every time its needed, and take down and pour there, it is coal fired from a pit underneath and takes around 5 days for their enormous investments. they also fire the bronze with coal also. its like stepping into history.
just goes to show how simple something can be, im sure ceramic kilns were once thus too.

[tobias]

I have fired clay sculpture in a really hot fire while camping. I let the wet clay sculpture dry first then put it on a rock ledge in the fire to get it up in temp. Then after a while I put it right in the fire. Then I bury it with coals and let it sit for an hour or so. Then slowly remove it from the heat. I would say that the whole process only took about three hours.
Now I am no ceramic guy but to test the first one I did I left it in water over night after firing and it was still hard as rock.

[krispee]

thanks guys.....
my main reason for using gas is that it is not as expensive to run as electric, that was a big concern of mine, the cost of running an electric kiln, and the fact that a gas bottle kiln can be moved if desired, where i live that`s a good thing.....
the Scutt kilns look very nice but i live in the uk, transporting it over here to the uk would be so expensive, and i could get the kiln i have in mind built for around £700/800 tops, although the change in design to a skeleton only would make it even cheaper......
i have previously got my sculptures fired by a friend who has a gas fired kiln [bottle] and he doesn`t have any problems with it shutting down, runs out of gas pretty quickly but seems to run smoothly enough......
i`m thinking if you make sure the flames doesn`t get anywhere near the clay but is directed around with some ceramic plates it should heat it pretty evenly, ok not as good as electric i appreciate, but again i`m very concerned with the costs of running that type of kiln......i may have to use the larger bottles to make sure i don`t run out during a firing......

would you suggest that i use some kind of cement to make sure the bricks don`t come out?

Kris

[krispee]

also some people are treating the inside of their kilns with a wash of some kind, not sure what that is about....is that necessary?

Kris

[mantrid]

also some people are treating the inside of their kilns with a wash of some kind, not sure what that is about....is that necessary?

Kris

Ive built my own furnace and have done a bit of research on the subject. I think the wash you talk about would be to stabalize and strengthen the surface. A good link on building your own burner and furnace and other matters relating to melting metal etc is

http://backyardmetalcasting.com

it also has a very good forum

http://backyardmetalcasting.com/forums

The same technology will be used for building a kiln for firing clay too.