Rimas VisGirda on sat 17 sep 11
Hey Lili,
Welcome to the present and the world of low temp 05 hobby products... Bisqu=
ing at 04, to burn out the organics so that they don't mess up the 05 glaze=
fire is pretty standard and has been recommended by the clay suppliers for=
at least 15-20 years; and 03 is close enough to 04 to be negligible in res=
ults. In the 70's the white low fire clay I made was 50% ball clay and 50% =
talc... Never did like the 05 whiteware, reminded me of chalk and seemed pu=
nky. I think the high bisque/low glaze industrial system you are thinking o=
f is for things like bone china that is bisqued to around cone 5-6, then gl=
azed with to 06-07. I believe (old) Fiesta is done similarly although I' no=
t sure of the temperatures. The orange and red Hall Pottery work was porcel=
ain and high fired with a clear glaze, then sprayed with (red, orange) over=
glaze and fired to about 016...
The R2 clay is supposed to have a range of 05-2... and be OK for raku. That=
makes me think that it's a pretty open body, meaning at cone 05-03 it's ju=
st bisque. I've found that ANY high fire body is suitable for raku, even po=
rcelain although for porcelain it's advisable to wedge in some grog (if you=
want brown bits) or sand (if you want it to remain white) to open the body=
for drying prior to bisque purposes. And the reason any high fire body wil=
l work in raku is that at raku temperatures the clay is still in bisque for=
m, very soft and porous hence able to absorb thermal shock without breaking=
... Conversely, one can attain guaranteed crackle by taking any high fire b=
ody, bisquing it to 05-03, slapping an 05 glaze on it and firing to 05, it =
is guaranteed to crackle. If you want the crackle to show up, you can take =
the piece hot out of the kiln and stick in a bucket of combustibles, shut t=
he lid and the carbon released from the combustibles (because
there's no oxygen to burn it) will permeate the exposed body and being ver=
y fine get into the crackle and turn the body at the crack black. If you do=
n't want to do the smoke thing, you can let the kin cool then take the piec=
e and paint it with lampblack or India Ink, let it dry and wash it off, voi=
la room temperature raku... So my suspicion would be that the R2 clay the p=
erson is using is still open at 05... Attached find a piece of room tempera=
ture raku...
I used to tell my students what the difference was between crackle and craz=
ing...
Crackle is if you like it
Crazing is if you don't
-Rimas
p.s. I'm thinking maybe you had a "senior moment" when you wrote your rant.=
.. that's OK, people our age are allowed to have that happen every once in =
a while...
Bonnie Staffel on sun 18 sep 11
When I was working with my low fire copper red glaze, mainly a frit =3D
based
recipe, I didn't like the crazing that went on when I did the whole =3D
piece at
Cone 04. So at the time, I had a spray booth and lots of equipment to =3D
work
with. So I high fired the porcelain to Cone 9/10 unglazed, then when =3D
heated
I dipped it into a coating of the glaze. When that dried, I spayed on =3D
more
coats of glaze as well as spraying on the copper carbonate. Fired to =3D
Cone 04
for the glaze, reduced on the cooling end, had perfect pots with no =3D
crazing
and the frit glaze also fired beautifully at the 04 temp. I don't see =3D
why
modern commercial glazes could not be treated in a similar fashion. It =3D
takes
some time, but the results are perfect. When I was using flower pot red =3D
clay
from a local mine, the fritted glaze didn't seem to craze on the pots =3D
that
were bisque fired to Cone 04 and glaze to the same temperature. It has =3D
been
a long time since I worked with the low fired clay, but I do remember =3D
firing
it to Cone 1 on occasion when I wanted a very hard basic pot.=3D20
=3D20
Now I don't have a spray booth, nor the room to do the things I used to =3D
do.
So I have moved on to smoke and trash can firing which satisfies my
exploring mind.
=3D20
Regards, Bonnie
=3D20
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Introduction to Wheel Work
Charter Member Potters Council
=3D20
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