Dawnisaacs@AOL.COM on mon 13 may 02
My question is simply is would it be ok to only partially glaze the surface
of some mugs with transparent glaze, leaving say a quarter of the surface
(red earthenware) unglazed, simply as I like the look of it. Or would this
make it no good for holding liquids. It has been fired already to 1060
bisque
and I would need to fire it again.
Thanks for your response.
Dawn
Timakia@AOL.COM on mon 13 may 02
Dawn, if your clay is vitrified(the fluxes melted together) then it will
hold
liquids. Clay by itself never become as glassy as a well fired glaze itself.
There is always at least a 3% absorbtion left. Unless you have hazardoud
materials in you clay, it will not be unsafe, but it might not be very clean
after you used it once, since you will not be able to get it clean enough
with soap and water.
Regards.
Antoinette.
Antoinette Badenhorst
http://hometown.aol.com/timakia
105 Westwood circle
Saltillo, MS
38866
Snail Scott on mon 13 may 02
At 09:19 AM 5/13/02 EDT, you wrote:
>My question is simply is would it be ok to only partially glaze the surface
>of some mugs with transparent glaze, leaving say a quarter of the surface
>(red earthenware) unglazed, simply as I like the look of it. Or would this
>make it no good for holding liquids.
It would not be worse for holding liquids than
it would have been if fully glazed. (I assume
the inside surface will be fully glazed in any
case.) The difficulty with earthenware is that
the almost-inevitable crazing allows moisture
to penetrate into the clay, accelerating the
crazing process and becoming a bit of a hazard
in the microwave. Having a portion of the outside
surface unglazed will simply allow moisture to
penetrate more easily, but it wouldn't be much
worse than a dry-footed piece. It could even be a
good thing, since any moisture which penetrates
might have an easier time evaporating out. I
wouldn't put such work in the dishwasher, but
that's true of any earthenware.
-Snail
Jeff Tsai on tue 14 may 02
Let me once again totally agree with Snail. If you still plan to glaze the
entire interior of the mug, then the mug is no less safe than if you had
left
the foot unglazed only. You could burnish the unglazed surface to decrease
its absorbancy, but that really wouldn't help much.
However, Antoinette noted that "if your clay is vitrified, then it will hold
liquids. Clay by itself never become as glassy as a well fired glaze itself.
There is always at least a 3% absorbtion left."
This is not probably true in your case, Dawn. At 1060 degrees C, most
eartenwares are still much more porous than 3%. To my knowledge, most people
working with functional eartenwares fire to about the range you are, and
most
of their clays retain a porosity of between 8-15%. 3% porosity is more
common
among stoneware potters firing to cone 9 or 10, but again, these are
generalizations. There are porcelain clay and glazes that I've heard of
that,
fired to maturity, have only a 1% porosity.
Whatever...do what you want, but before you sell it, test it. Snail says not
to put it in a dishwasher...well, I will disagree with him only there. After
you do this piece, test it in a dishwasher. run it through with the next ten
loads of dishes and see how badly the interior glaze begins to craze after
each load. Figure out if you feel this is acceptable, and then give warning
to those who purchase your work accordingly.
-jeff
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