Alisa and Claus Clausen on thu 31 aug 00
Dear Clayart
Recnetly at a seminar I saw Les Manning, Canada, throw a number of =
different clay bodies combined in a specific arrangement with color to =
echo the landscapes he lives in . Now that I have my slips and glazes =
hanging on together, I wanted to try this.Why stay happy with something =
that took a year to figure out and it works every time. On my to do =
list is always seemingly whole new set of complicated problems.
I used a white body, a little short, with stain and oxide colored =
porcelain coils packed in to make the color stridations. The whole
piece of throwing clay was then topped with a solid white lump of =
porcelain. Thrown, and and later trimmed all the way down the vessel,
so appear the colored stridations, with a snowy cap as the rim. Looks =
good. Dried extremely slowly, and bisqued and it is all intact with
no cracks.
The stoneware shrinks at 11% and the porcelain at 18%. I did not expect =
it survive the drying stage.
I fired on piece to cone 6 with Chris Wolff Cream Gloss
13 GB
8,7 Whiting
60,90 Custer
8,7 Kaolin
8,7 Flint
11,5 RIO
Pot looks good, colors damped by glaze, gives cloudy like coverage over =
a sunset of colors underneath.
Next day...ping. Crazing on lip and some long cracks down the side. =
Not at all overall, but some and not
good enough to use.
Problem to solve:
Despite my skeptism that the clays would not dry without cracking due to =
their differences in shrinkage rates,=20
they did fire without cracking.=20
I am thinking that I need to find a glaze that fits the porcelain, =
because that is the problem.
I tested the same glaze on a small piece of the just the porcelain and =
it is still not crazed.
Could be the larger piece has to be absolutely cooled in the kiln before =
removing. Was=20
removed at 150c.
OR, I need to use a porcelain that shrinks less (is 15% enough of a =
differnce) and try the Cream Gloss again.
I can use a glaze that better fits the porcelain porcelain portions of =
the pot, but will I expect it craze on the stoneware portion?
(glaze will not contract too much over porcelain, but will it be not =
contracted enough (to big?) over the stoneware?
I am trying to sort out the variables again, and would like to know that =
when combined clays with differing shrinkage rates will give a problem,
it is usually in the initial stage of drying, or will it show up mainly =
later in the glaze firng ?(Les had some cracking problems in the glaze =
firing, but
he fires to cone 10 and I am only going up to 6)
If a glaze crazes, it is usually (always?) due to a clay body shrinking =
more than the glaze can contract?
I can use a white stoneware and color it and get mainly the same =
results, but I would like to try the porcelain stridations.
Best regards,
Alisa in Denmark
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