Cameron Harman on tue 7 oct 97
Black coring is a commercial problem as well. Even white porcelain
insulators or yellow steatite bodies get it.
It is, indeed, a problem of not oxidizing the body properly during
firing. In a red clay boy, for example, Fe2O3 reduces to Fe3O4 and
reacts with the free silica to make a black iron silicate that is very
glassy and not very strong. There is suffiicient organic in any ball
clay to cause the problem. If you fire long enough below 900 F you will
burn it out.
It is possible to work out the peak temperature for the burn out , but a
kllittle trial an error goes a long way.
Remember it is the presence of organic material that causes the problem
because it robs oxygen from the other minerals if it can't get oxygen
any other way, so if you give the kiln plenty of air between 400 and 900
F you won't have a problem.
Bye
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Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
e-mail kilns@kilnman.com
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
see our web site at http://www.kilnman.com
THE place for solutions to ALL your kiln and drier problems
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