inge nielsen on tue 22 mar 11
Hello,
Greetings from Taiwan! I am very happy to have recently joined this forum.
In the studio where I study, we have a problem with the Kuan (Guan) crackle
1 glaze from John Britt's excellent book on high-fire glazes. The first
tests on dark clay were gorgeous. But ever since (on the same clay body and
in different firings), the glaze comes out overall blackish with maybe a
small patch of white ice crackles. My teacher suspects it sucks up smoke in
the reduction. Is this a common problem with a simple cure? The other
students are ready to try firing in a box, but hope there is a more
practical and economical solution.
The recipe is:
Custer feldspar 79
Whiting 9.5
Silica 9,5
Bone ash 2
bentonite 2
We bisque to 900 degrees, then fire with electricity to 950 degrees and
reduction thereafter to 1260.
Any advice appreciated.
Regards,
Inge Nielsen
John Britt on tue 22 mar 11
I would say you just have too strong reduction.=3D20=3D20
You could try saggars with or without lids.=3D20
Or try to fire them in some oxidizing pockets of the kiln (if you have a=
=3D
ny). Maybe=3D20
near the back by the flue or ??? You could try putting bisque pots cut in=
=3D
half=3D20
around an area ( or soft fire bricks) to make a shelter for them from the=
=3D
heavy=3D20
reduction (maybe on the bottom shelf) .=3D20=3D20
Or try rebisque firing them to burn out some of the carbon (it doesn't al=
=3D
ways work=3D20
but worth a try).
John Britt
Ron Roy on wed 23 mar 11
Hi Inge,
Not much clay to help suspend that glaze - you are probably getting
variations because it will not stay suspended properly when you apply
it.
I is also very high in KNaO so it may be acting like a shino glaze and
carbon trapping.
It could be the kind of spar you are using - some spars leach sodium
into a glaze and help deflocculate it making it hard to keep stirred.
If that is the case then flocculating the glaze with a small addition
of epsom salts may cure the problem.
Let me know if you want to try that.
I would also be helpful to know the analysis of the spar you are using.
RR
Quoting inge nielsen :
> Hello,
>
> Greetings from Taiwan! I am very happy to have recently joined this forum=
.
>
> In the studio where I study, we have a problem with the Kuan (Guan) crack=
le
> 1 glaze from John Britt's excellent book on high-fire glazes. The first
> tests on dark clay were gorgeous. But ever since (on the same clay body a=
nd
> in different firings), the glaze comes out overall blackish with maybe a
> small patch of white ice crackles. My teacher suspects it sucks up smoke =
in
> the reduction. Is this a common problem with a simple cure? The other
> students are ready to try firing in a box, but hope there is a more
> practical and economical solution.
>
> The recipe is:
> Custer feldspar 79
> Whiting 9.5
> Silica 9,5
> Bone ash 2
> bentonite 2
>
> We bisque to 900 degrees, then fire with electricity to 950 degrees and
> reduction thereafter to 1260.
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