Test Kiln?
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Subject Author Date
Test Kiln? Bill DeWitt 07-15-2006
Posted by Bill DeWitt on July 15, 2006, 3:12 pm
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In my process of trying to test out the wild clay I spoke about earlier, I
have built a small test kiln. It has changed shape several times in two
days, but the basic premise is a two inch cube of furnace space surrounded
by firebrick, heated by a propane torch. It quickly reaches an undetermined
but fairly hot condition.

I say undetermined because I don't have any experience working with a kiln,
previously I have simply hired someone to fire my pieces. Here are my test
results, maybe someone can tell me about how hot it's been getting and maybe
how I can improve it.

Commercial clay fires completely. Comes out with a ringing sound and breaks
like a tea cup. My wild clay comes out changed in color, but brittle and
granular with a tendency to dissolve in water.

(On a side note, I did get a small portion of the wild clay to turn to
glass, (after washing, sifting and grinding) but it contracted into beads
both by itself and as a glaze. Either I am using it wrong or it is dirt.)

Unfortunately, it will be days/weeks until I get out to the ceramics supply
in Rutland, so I don't have cones or a selection of glazes to work with...
but maybe there are more tests I can run? Common substances with known
properties?

Also, my most recent design is simply a cube with a torch in one corner and
a chimney on top. My thought was to have the flame circle the walls in hopes
of transferring a significant portion of its heat before escaping up the
draft. The result is that all visible walls get red hot before the test
object does. I could rearrange things to have the flame play right on the
object, but am I correct in thinking that indirect heating is preferable? I
have made a piece of clay in a shape to more smoothly redirect the flame
around the first corner but it is far from ready to put to the fire...

Not a pressing question because I think I really will be getting a real kiln
fairly soon, but I will appreciate any input.

TIA, Bill



Posted by Urbana on July 16, 2006, 3:27 am
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Dear Bill,
You should make a cone pack and put it in there so you can know to
what cone temp you are heating. It doesn't matter if it turns to glass
or not if you don't know what the temp is when the change occurs. I
like what you are doing though.

Another way that you can tell what the approximate temp of the kiln
is- is to look at the color of the atmosphere in your kiln... To do so
you will need to be able to peek inside.

Good Luck and keep melting things!
:>
Urbana


Posted by Bill DeWitt on July 16, 2006, 10:55 am
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> Dear Bill,
> You should make a cone pack and put it in there so you can know to
> what cone temp you are heating.

"Make a cone pack"... nothing in my book about making a cone pack. I
have seen them, four or five cones on a block, but I assumed they were made
of differing clays of known quality. That would be outside my skillset at
this point. OH... just looked it up on the web... I will have to wait until
I go to Rutland to get some cones, by then I may have a real kiln.

> Another way that you can tell what the approximate temp of the kiln
> is- is to look at the color of the atmosphere in your kiln... To do so
> you will need to be able to peek inside.

I can peer down the chimney, but I have nothing against which to compare
what I see.

> Good Luck and keep melting things!

Thanks! I am, at the very least, learning things about kilns which
previously were just words on paper. Like "exploding clay".... 8-)

My Wild clay, which makes a nice copper color BTW, is mostly useless.
Tests for the day include mixing it into a varying amount of commercial clay
to see if it ruins the clay completely or lends it color to make a working
substance.



Posted by Bob Masta on July 16, 2006, 1:47 pm
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>Dear Bill,
> You should make a cone pack and put it in there so you can know to
>what cone temp you are heating. It doesn't matter if it turns to glass
>or not if you don't know what the temp is when the change occurs. I
>like what you are doing though.
>
> Another way that you can tell what the approximate temp of the kiln
>is- is to look at the color of the atmosphere in your kiln... To do so
>you will need to be able to peek inside.
>

Since the test kiln is only a 2 inch cube inside,
that doesn't leave much space for a cone pack
*and* a test piece. How about a thermocouple
instead? You'd need a type K thermocouple
(or some type K wires that you could use to
weld your own thermocouple), plus a digital
voltmeter (DVM) and a type K voltage-temperature
chart. The DVM should have a 200 mV full-scale
range. (The type K will output 50 mV or less.)
You can get a cheap DVM for under $10 (sometimes
under $5) from places like Harbor Freight.
The trick might be finding the thermocouple or
wire. You might check if there are any likely
businesses near you that deal with industrial
furnaces or the like. One possibility might even be
a home furnace thermocouple... I have read that
they are type K. (But apparently some are not
even real thermocouples, so be sure to check.)
These are only a few bucks at the hardware store.
What I don't know is how long they will last in this
use. When they finally go bad in my furnace, the
sheath often looks melted.

You can get type K (or any other type) thermocopuple
voltage-temperature tables from the Web. I think
the National Bureau of Standards is one place.

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

Posted by Steve Mills on July 16, 2006, 5:19 pm
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Dear Bob,

In the UK where Bill lives, we can get cheap Type N Thermocouples on the
net which have a much higher range (1300oC) than Type K which ceases to
be accurate over 1200oC.
The place to look in the UK is:

<http://www.tc.co.uk>

This company also does multi-type indicators which by UK standards are
reasonably priced at around 70 pounds. I have a couple and wouldn't be
without them. I use them in my home built test kiln.

Steve
Bath
UK




>Since the test kiln is only a 2 inch cube inside,
>that doesn't leave much space for a cone pack
>*and* a test piece. How about a thermocouple
>instead? You'd need a type K thermocouple
>(or some type K wires that you could use to
>weld your own thermocouple), plus a digital
>voltmeter (DVM) and a type K voltage-temperature
>chart. The DVM should have a 200 mV full-scale
>range. (The type K will output 50 mV or less.)
>You can get a cheap DVM for under $10 (sometimes
>under $5) from places like Harbor Freight.
>The trick might be finding the thermocouple or
>wire. You might check if there are any likely
>businesses near you that deal with industrial
>furnaces or the like. One possibility might even be
>a home furnace thermocouple... I have read that
>they are type K. (But apparently some are not
>even real thermocouples, so be sure to check.)
>These are only a few bucks at the hardware store.
>What I don't know is how long they will last in this
>use. When they finally go bad in my furnace, the
>sheath often looks melted.
>
>You can get type K (or any other type) thermocopuple
>voltage-temperature tables from the Web. I think
>the National Bureau of Standards is one place.
>
>Best regards,
>
>
>Bob Masta
>dqatechATdaqartaDOTcom
>
> D A Q A R T A
>Data AcQuisition And Real-Time Analysis
> www.daqarta.com
>Home of DaqGen, the FREEWARE signal generator

--
Steve Mills
Bath
UK

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