Cameron Harman on tue 9 jun 98
As usual Ron's comments are well taken. I am jumping in to add
what I hope will be some further clarity to the issue.
In the American Ceramic Industry it was determined quite a long
time ago that there had to be some definitions that everyone could
agree to so that we all knew what each other was talking about. so
as a result here are some definitions that have been in common use
since before I was born.. let's not say how long ago that was, but
suffice it to say that few, if any are alive today that were
around when it happened.
1. Ceramics .. any material that is inorganic, non-metallic. You
may be interested to know that includes glass, cement, plaster,
etc. as well as traditional ceramics.
2. Grades of ceramic bodies ... china or porcelain is defined as
having less than 0.1% water absorption after firing
semi vitreous (once called semivit) is defined as having
more porosity but less than 3% after firing
earthenware is defined as being any porous utilitarian
ware.
3. china is fully vitrified (usually translucent, but not
necessarily) where the glaze is fire to a lower temperature than
the vitrified ware.
porcelain is fully vitrified where the glaze is fired to the
same or higher temperature as the vitrified body.
The last two definitions above apply most frequently to
utilitarian ware. One does not spear of sewer pipe as being
earthenware or porcelain, etc. However, it is interesting to note
that there was a time when sewer pipe would "sweat". That was when
it was salt glazed. It was determined that the salt glaze actually
deteriorated the clay body and led to more porosity that would
have been there without the salt glaze. That was exactly opposite
to the generally accepted thinking. It was really hell getting the
local authorities all over the world to accept the fact that salt
glazing was a bad thing not a good thing. You know the thinking,
don't let the truth get in the way of good bureaucratic thinking.
If one is making an earthenware body you should expect it to
"sweat" after all that is the way they got cool water in the
Southwest many years ago. A poor glaze can cause the same thing..
--
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Cameron G. Harman, Jr. President Ceramic Services, Inc.
215-245-4040 fax 215-638-1812 visit us http://www.@kilnman.com
1060 Park Ave. Bensalem, PA 19020
THE place to go for answers to all YOUR kiln and dryer questions
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