Peter Jones on sun 11 oct 09
I agree with all that various respondents have said about your
thermocouple calibration. Any connection points between the
thermocouple, the wire to the gauge and the gauge itself can
introduce resistance due to corrosion of the connection points.
Thermocouples themselves get major corrosion over time and simply
fail all together at some point. There's also on other thing to
consider: the temperature you fire to, according to your
thermocouple, and the cone temperature equivalent are rarely the same
thing to begin with. A cone measures the amount of heatwork over a
given period of time whereas a thermocouple measures the temperature
(in farenheit or celsius) at any given moment. As such, a cone is
the only way to truly measure the condition of the glaze and clay
body. If you go to this website and download the chart provided by
Orton Ceramics, you'll see the difference that heat applied over time
has on the true temperature that the cone bends at:
www.ortonceramic.com/resources/pdf/wall_chart_degreeF.pdf . You can
see that a cone 10 fired at a faster rate is up to 59 degrees hotter
in temperature than firing at a slower rate.
Just one more thing to ponder in the complex world of ceramics....
Peter Jones
Mountain Street Pottery
80 Mountain St
Camden, ME 04843
pjcaver@gwi.net
www.pjcaver.com
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