[Clayart] Bad Bowl Test

Paul Gerhold gerholdclay at gmail.com
Sat Nov 12 14:48:10 EST 2016

I have a bowl as previously mentioned that when microwaved gets too hot to touch so I ran some tests.  Let me first say the bowl has a vet dark iron glaze on outside, a crazed turquoise/ transparent glaze on the inside, appears quite dense, is not overly thin and is made of a white clay.  

First Test- weighed bowl at 449 .0 grams and then held in a six hundred degree   
                    Kiln for about twelve hours and weighed hot out of kiln.  Weight 448.5 grams so no significant absorption of water.  Note craze lines turned black indicating probable carbon from food particles in craze lines.

Second Test- put in microwave with a glass of water inside bowl and microwaved for 45 seconds.  Bowl did not heat at all. This is the test in my microwave book for microwave compatibility of  a vessel.  Conclusion would appear that the vessel is not absorbing significant microwave radiation.

Third test- put water in bowl to about half the height and microwaved for 90 seconds.  Liquid in bowl 165 degrees and bottom of bowl to hot to touch.  Very top of bowl much cooler.  Conclusion the bowl is very rapidly transferring heat from the liquid to the surface.  In other words whatever the clay and firing temp the result is an extremely high heat transfer coefficient.

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