Gary Beckwith on tue 29 may 12
Hi all,
I am using a gas kiln to bisque fire. Have not had any problems so far. O=
ver
the weekend I did a cone 010 bisque using cone 10 B-Mix which had Terra Sig
applied. The Terra Sig surface shows crazing. It seems to be well-adhere=
d to
the bodies of the pieces. I had wanted to use them for horse hair so I'm u=
nsure
how they will look now. I ran the kiln for 8 hours with just the pilot to
drive out any moisture, and then took another 7 hours to get to temperature=
. I
didn't give any "soaking" period once I reached cone, I just shut the gas
burners off. Would that have helped? I did try to slow the cooling down a=
s
much a possible by stacking layers of kaowool on top of the kiln. It's an=
old
Thermolite updraft with 4 MR750 burners. Inside dimensions 28-30. Other th=
an
the crazing, the pieces came out perfect, no cracks. Any suggestions would=
be
greatly appreciated.
Thanks
Gary Beckwith
Beckwith Pottery
Auburn, CA
Sumi von Dassow on wed 30 may 12
Gary
I get crazing now and then with terra sig in a pit firing. Usually it
doesn't craze during the bisque firing but just in a pit or saggar
firing when the temperature rise is much faster. If it does craze in the
bisque-firing it often will peel off in places in a subsequent pit or
saggar firing. My observation is that this crazing occurs when the terra
sig is just a bit thickly applied. If it is applied too thick, the
crazing turns into peeling. So it is possible your crazed surface will
peel after a horse-hair firing but the only way to find out is to do it!
Considering that your horse-hair firing is going to be much faster than
the bisque-firing, I don't think you need to worry about bisque-firing
slower, but if you get peeling then you need to apply less terra sig -
fewer coats or thin it down more or both - next time. Oh, and I always
let a pot dry 24 hours if possible after applying the terra sig before
bisque-firing, although I know other people who don't take that
precaution. I find if the pot is at all damp when it is subjected to
heat, even a slow warm-up, the terra sig is more likely to peel.
Sumi
> Hi all,
>
> I am using a gas kiln to bisque fire. Have not had any problems so far. =
Over
> the weekend I did a cone 010 bisque using cone 10 B-Mix which had Terra S=
ig
> applied. The Terra Sig surface shows crazing. It seems to be well-adhe=
red to
> the bodies of the pieces. I had wanted to use them for horse hair so I'm=
unsure
> how they will look now. I ran the kiln for 8 hours with just the pilot =
to
> drive out any moisture, and then took another 7 hours to get to temperatu=
re. I
> didn't give any "soaking" period once I reached cone, I just shut the gas
> burners off. Would that have helped? I did try to slow the cooling down=
as
> much a possible by stacking layers of kaowool on top of the kiln. It's =
an old
> Thermolite updraft with 4 MR750 burners. Inside dimensions 28-30. Other =
than
> the crazing, the pieces came out perfect, no cracks. Any suggestions wou=
ld be
> greatly appreciated.
>
>
> Thanks
> Gary Beckwith
> Beckwith Pottery
> Auburn, CA
>
>
Allyson May on thu 31 may 12
I agree with Sumi. Usually when I get crazing it is due to the terra =3D
sig being a little too thick in an area. Thin it down or use fewer =3D
coats. =3D20
Some times, in a naked raku firing or a saggar firing, crazing of the =3D
sig can be quite beautiful. That is, of course, if it doesn't peel in =3D
the later firing. =3D20
Another thing to check is if your pots were dusty or you handled them =3D
with your bare hands. Dust, dirt, fingerprints can all cause terra sig =3D
to do funny things.=3D20
I always make sure my sig is completely dry before the bisque. I never =3D
force dry terra sig or slip (i.e., the kiln, oven sun...). My pots are =3D
placed in a room near a dehumidifier for at least 48 hrs. prior to =3D
bisque.
Ceramic Arts Daily just had a video clip on terra sig. A portion of it =3D
talks about the specific gravity of your terra sig. Finding the =3D
specific gravity can help you determine if your sig is too thick or =3D
thin.
If you don't have graduated cylinders and a triple beam balance at your =3D
disposal try making a hydrometer out of a McDonalds drinking straw. I =3D
use one and it works well. I teach my workshop students how to do it. =3D
Just Google "drinking straw hydrometer" for full instructions. If you =3D
have trouble let me know and I will try to send you the info. Hope this =
=3D
helps!
Peace,
Allyson May
www.stoneycreekpottery.com
| |
|
