Martin Rice on sun 6 oct 02
Hi, All:
Recently I wrote about my first "real" glaze firing, that is, with
decoration that I worked hard on to begin developing what I hope will
eventually be an original style.
Of course the problem was that everything crazed badly. I got many, many
responses from you trying to help me with this problem and making lots of
suggestions.
One thing I noticed in that first firing and mentioned was that I had also
done a piece in which I used the prepared Duncan glaze, water, slip, and
cobalt oxide and that this piece was the only one that did not craze.
Some of you suggested that the slip might have given me a better fit. So the
day before yesterday I prepared another test and fired it yesterday. I think
the results are quite interesting.
I prepared the clear overglaze the same way the colored glaze was prepared:
1 part Duncan clear glaze, 1/2 part water, 1/2 part slip and, of course,
didn't add the oxide. The first three test pieces had the Duncan underglaze
covered with two thin coats of my new slip glaze. No crazing whatsoever!
(Well, there's a slight exception to that I'll mention later).
The fourth piece I did exactly the way I did the original firing, that is,
underglaze covered by the diluted clear glaze without slip. Totally crazed,
just as in the original firing.
That certainly says something. The slip seems to have made all the
difference as far as crazing goes.
BUT....when I was ready to glaze the fifth piece, I noticed that my slip
glaze seemed to be thinner than the Ducan glaze with water alone. So I added
more water to that glaze. Lo and behold, no crazing! So, the same glaze that
crazed so badly, didn't craze at all when it was thinner. Well, I guess that
says something, too. I actually prefer this because I'm looking in this
series for a high gloss, and this is much glossier than the glaze with slip.
About the slight exception: I said that the pieces that had the slip glaze
on them didn't craze at all. That's not quite true. There is a tiny bit of
crazing on the outside of the footrings of all these pieces. I had glaze on
the bottom of the footrings which I washed off with a wet sponge. My guess
is that the foot ring then had absorbed water and that is probably why only
it has crazing.
I feel this has been a very profitable test. There were several other
variations where I put the slip glaze on and then the underglazes on top of
that and also on some pieces another coat of slip glaze on top of the
underglaze that was on top of the slip glaze :-) Didn't care for those at
all.
Lots more testing to do. For one thing, I need to measure the specific
gravity of these watered down glazes so that eventually I can reproduce the
results easily and more exactly. My test kiln should be here in about two
weeks which will enable me to do a lot more testing a lot more quickly.
Thanks to all who wrote me with suggestions about my problem.
Regards,
Martin
Lagunas de Barú, Costa Rica
www.rice-family.org
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