Underfired? Oh My! Now What?

Well, the pyrometric cone didn’t melt (bend) in my latest glaze firing.  This has never happened before. It could simply mean the cone was bad; though, very unlikely.  More likely, it could mean the kiln never got to temperature (cone 6 = 2165 degrees Fahrenheit – 2269 degrees Fahrenheit) and therefore the stuff in the kiln was underfired. Sigh.  I’m anticipating a much different glaze outcome: more of a matt finish rather than a shiny finish.  So, I must wait until the kiln cools off enough to be able to assess the problems.

What is a pyrometric cone?  Cones are “three sided pyramids made from a range of compositions each with a reference number corresponding to a certain heat work.” (love the Wikipedia!)  A cone us a unit of measure: heat and time (heat work).

A cone in a kiln sitter. (photo from lakeside pottery.com)

When the cone melts or bends, it means the temperature (heat work) has been reached inside the kiln.  And when this happens, the kiln shuts off.

Cone in kiln sitter melted. (photo from lakeside pottery.com)

In my case today, the cone didn’t melt or bend leaving the pottery underfired.  As to what kind of results this will have on the glazes, I’ll just have to wait and see.  Keeping fingers crossed that some pots may be salvageable. When the kiln cools, I have some sleuthing to do to find out why this happened.  Heating element gone bad? Short in the one of the three prongs of the plug cause less voltage into the kiln?  Stay tuned!

UPDATE:  Okay…I just peeked!  Things may not look as bad as I first thought…

Sources:

Big Ceramic Store

Lakeside Pottery

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