ronroy@CA.INTER.NET on sun 19 feb 12
HI Gene,
Paper in the clay? That takes a long time to burn out - if you don't
have a vent running leave both spys open and fire to 04 - maybe slow
down a bit - that sounds like a classic case of carbon reduced iron in
the bisque leading to overfired clay - what colours are the clay inside?
RR
Quoting mudduck :
> Opened the gas kiln Saturday and had a lot of bloating. Very large
> blisters, when broken open seemed to have sand or some kind of grit
> inside the blisters. I've had some of this in the past but never to
> this extent.
>
> It must be something I'm doing because I had two different clay
> bodies in the firing and both had bloating. I had Standard 119 and B
> mix cone 10 with paper and grog in the firing.
>
> I bisque fire in an electric kiln to cone 07 in 10 1/2 hrs with a 15
> min. hold at the top. Then I glaze fire in a down draft 45 cu. ft.
> gas kiln with light reduction. The kiln is a Minnesota flat top with
> an arch. In fact I fire as close to neutral as I can up to 2000F
> degree and then a light reduction to the end. My glaze firing is 11
> 1/2 to 12 hrs. The kiln takes 2 days to cool.
>
> I'm going to fire again this week and would like to figure out what
> I'm doing to cause the bloating.
>
> Thanks for any help!!!!
> Gene
> mudduck@mudduckpottery.net
> www.mudduckpottery.net
>
mudduck on sun 19 feb 12
Opened the gas kiln Saturday and had a lot of bloating. Very large =3D
blisters, when broken open seemed to have sand or some kind of grit =3D
inside the blisters. I've had some of this in the past but never to this =
=3D
extent.=3D20
It must be something I'm doing because I had two different clay bodies =3D
in the firing and both had bloating. I had Standard 119 and B mix cone =3D
10 with paper and grog in the firing.=3D20
I bisque fire in an electric kiln to cone 07 in 10 1/2 hrs with a 15 =3D
min. hold at the top. Then I glaze fire in a down draft 45 cu. ft. gas =3D
kiln with light reduction. The kiln is a Minnesota flat top with an =3D
arch. In fact I fire as close to neutral as I can up to 2000F degree and =
=3D
then a light reduction to the end. My glaze firing is 11 1/2 to 12 hrs. =3D
The kiln takes 2 days to cool.
I'm going to fire again this week and would like to figure out what I'm =3D
doing to cause the bloating.
Thanks for any help!!!!
Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net
Liz Gowen 1 on sun 19 feb 12
Gene, I used to use standard 119 as a cone 6 clay. This is one of those
clays folks were talking about with too wide a firing range. Standard list
it as a cone 6 to 10. When I used it at ^6 I think it was a bit under fired=
,
would absorb water and get hot in the microwave. I also lost a number of
pieces when I put something from the freezer to the microwave on something
made with 119. I think this is too wide a firing area for any one clay and
perhaps the bloating is it melting because you fired to its upper limit. My
bet is this is about a cone 8 clay. B mix I have used at cone 10 usually di=
d
ok if fired once but had some bloating if I fired it a second time to cone
10. If your glazes can be fired at ^9 perhaps you may want to try it there=
.
It sounds like you have already made the pieces. I do bisque to cone 04
which I slowed down a bit to make sure to get rid of all the organics, but =
I
am kind of guessing the clays are being over fired at cone 10...Liz Gowen
Subject: Help I'm bloating
Opened the gas kiln Saturday and had a lot of bloating. Very large blisters=
,
when broken open seemed to have sand or some kind of grit inside the
blisters. I've had some of this in the past but never to this extent.
It must be something I'm doing because I had two different clay bodies in
the firing and both had bloating. I had Standard 119 and B mix cone 10 with
paper and grog in the firing.
I bisque fire in an electric kiln to cone 07 in 10 1/2 hrs with a 15 min.
hold at the top. Then I glaze fire in a down draft 45 cu. ft. gas kiln with
light reduction. The kiln is a Minnesota flat top with an arch. In fact I
fire as close to neutral as I can up to 2000F degree and then a light
reduction to the end. My glaze firing is 11 1/2 to 12 hrs. The kiln takes 2
days to cool.
I'm going to fire again this week and would like to figure out what I'm
doing to cause the bloating.
Thanks for any help!!!!
Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net
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