Now that most kilns have a computerized controller it’s become easier
to control the kiln’s temperature. But, is the controller’s readout
accurate? With so many varieties of bronze, copper, and silver metal
clays, it has become important to know if your kiln’s temperature
reading is correct. Otherwise, you may have problems with the clay not
sintering correctly or getting too hot and melting. Additionally, the
kiln should be tested for hot spots and cooler spots. Every kiln is
different.
Testing can be done by using a pyrometer (which is how I used to adjust
my kiln’s temperature before there were controllers) or by using kiln
pyrometric cones. The pyrometric cones are supposed to bend when heated
to a specific temperature for a certain amount of time. That means that
pyrometric cones give a temperature equivalent; they are not simple
temperature-measuring devices. According to a pyrometric cone
manufacturer, cones have over 20 variables that can affect the cone’s
bending, including the cone's composition, particle size of raw
materials, type of forming process, moisture during forming, density of
the cone, geometry of the cone, setting height, and angle and the
heating rate. Atmosphere also affects bending behavior. Wow, that’s a
lot of variables! So, let’s look at testing with a pyrometer or a kiln
test kit.
I used the
kiln test kit sold
by the PMC Connection. According to experts, the average kiln
controller is accurate to ±10°F (±5.5°C) so keep this in mind while
testing. Additionally, run the test several times but move the
thermocouple to different areas of your kiln. Place it towards the back,
near the front, off to each side, and etc. Test at different
temperatures. I conducted tests at 1110˚F, 1200˚F, 1290˚F, 1470˚F,
1560˚F, and 1650˚F. I found that both readouts were within a few degrees
of each other until the temperature got up to 1650˚F. Then they were
off by 10˚F! So, I added another thermocouple from my casting kiln. All
three read different degrees but were within the accuracy range.
Now I know why my PMC3 clay had a crystalline look to it when I fired it
at 1650˚F; it was getting too hot! So, now I lower the temperature of
my kiln by a few degrees when setting it at 1650˚F.
The Test Kit Includes:
- Sensor reader (tester)
- 9V Battery
- K-type thermocouple TP-02A
- K-type thermocouple TP-03
- Case
Use the TP-02A thermocouple (larger one) for testing your kiln. It has a temperature measuring range of (-58˚F to 1650˚F).
The Steps
1. Install the 9 V battery into the unit’s back.
2. Insert the plug into the bottom of the sensor reader making sure the plug’s polarity matches with the sensor’s polarity.
3. Insert the thermocouple into the kiln.
Caution: Don’t insert it past larger ceramic end or the wires will burn!
4. Place the thermocouple near the kiln’s thermocouple for the first run of testing.
5. Turn on the kiln and set it to hold at the test temperature for at least 15 minutes.
The sensor reader can read in Fahrenheit (F) or Centigrade (C). Turn it
on by sliding the button from the center (off position) to the F (if
measuring in Fahrenheit).
6. The sensor displays its reading. Allow it a minute to stabilize to
the temperature. Test at various temperatures. I found that my kiln was
accurate until it reached over 1350 (F).
7. When finished testing, turn off kiln and sensor reader and allow the thermocouple to cool before touching it.