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more questions/tiles warping

updated thu 15 oct 98


Autumn Downey on tue 13 oct 98

I am wondering if the warping of the tiles might be from the glaze having a
"tight" fit and contracting? This wouldn't affect a pot that had glaze
inside and outside. Perhaps if the tiles were thicker this wouldn't
happen? Or using a glaze with more expansion?

Which brings me to asking about the effects of surface tension of a glaze.
Could too high a s.t. cause dunting or would that be from too low an
expansion? I can't quite imagine what surface tension in a glaze means
especially if it's not quite the same as viscosity, which I gather it
isn't. How do these characteristics (surface tension, viscosity, low
expansion) play a role in crawling glazes?

At the moment nothing is dunting or crawling, so it's mostly just curiosity
prompting these questions. Thanks.

Autumn Downey

Cameron Harman on wed 14 oct 98

To Autumn,

There are some interesting things to say in answer to your query.
In the first place, you are correct that the glaze can warp a
tile, but ony a very, very thin tile, say less than 1/16th inch

As a means of measuring the relative thermal expansion of a glaze
one can take a fired ring, say one half inch wide and cut a 1/8
inch slice out of it then glaze just the outside. Fire the glaze
and measure the width of the open section after cooling. How much
more or less than 1/8 inch will give you an idea of the fit of
that glaze with that body.

Nearly always the warping of a tile is caused by drying, this is
true even when the warping shows up after firing.

Dunting of a ceramic body is unrelated to the glaze or glaze fit.
Dunting is a term that is not used professionally to describe any
of the defects of a glaze, therfore, I am not sure what you mean
to say in this regard.

I'll let some of the others comment on tension and viscosity.


Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
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