Elizabeth Herod on mon 25 nov 02
We had a raku firing yesterday, and I was not overly pleased with some of
the results. I=B9d like to know what other people=B9s thoughts are on the
subject.
Two of my pieces were porcelain, hand built, and marbled with colored clay,
using chrome oxide and copper carbonate. I used Bob Compton=B9s white crackl=
e
on the two pieces. Normally, the copper and chrome become metallic and
there is a nice crackle over the piece. This time there was no crackle,
where there should have been crackle, it looks like mildew, and on one of
the pieces, the entire side is copper.
The temperature was around 1900, kiln was packed tightly, and the outside
temperature was in the 40=B9s, no wind. Both pieces were waved around in the
air before being put into the can with sawdust, which in one case, really
flamed.
I think that the crackle did not crackle because the temperature might have
been a bit too low, and the excess copper was caused by another piece, clos=
e
by, and the copper molecules from my piece grabbed some of that other
copper. (It seems logical to me, but I am not a chemist)
As I study the pieces today, they have their own unique look to them,
probably never to be duplicated again. I=B9ve developed the attitude of
=B3whatever=B2 although I do keep trying to achieve certain results.
My other problem is the cracking, not only on the large wheel thrown pieces=
,
but also on the hand built pieces. My teachers have suggested that the
slabs of the cracked piece are too thin. (I just measured, and the cracked
piece is 1/4=B2 thick, whereas the pieces that are not cracked are thicker
(3/8=B2-1/2=B2), but also, they are smaller. 12=B2 as opposed to 9=B2. Wheel
thrown cracks are in the 9+ inch pots, never the smaller ones. These were
with raku clay).
At any rate, I=B9ll take some pictures, then make other ones, with slightly
different dimensions.
One more thought. Supposing that I threw a pot that had too much clay at
the bottom, but later trimmed it to be of the same thickness as the rest of
the pot, can this by itself cause cracking in the glaze firing? (I=B9m hopin=
g
that this should not be a problem in the future as I have since started to
really pull the clay up from the bottom. This pot was thrown in the summer
and I totally forgot about it for the previous raku firing)
Beth
Just a side note to the novices. I have been threw the thick and thin of
the pots, making things I did not want to make, i.e. Casseroles. I decided
to go on a cylinder kick, go into the studio and throw 6 cylinders, really
getting the clay up from the bottom. I went back down to 4 pounds of clay,
and measure out six balls of clay every time I do this. Three of the
cylinders, I=B9ll make into various shapes with ribs, and the other 3 will be
altered in some way. This has really helped me improve my throwing skill i=
n
a short space of time, and my pieces are larger than when I was using 5 and
6 pounds of clay. I also went back to stoneware and raku clay, feeling tha=
t
I=B9ll know when I=B9m ready to throw porcelain again.
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