Hendrix, Taylor J on wed 11 feb 04
Wellllllllllll Duck,
You might want to listen to the smart glaze monkeys, but if your
brave...
Blisters of the glaze only?
I'm just now getting this stuff pushed into my addled pate, so forgive
if it appears that I condescend. 'Taint so.
Could it be the low bisque temp not burning off burnoffables? Perhaps
it's the whiting still giving off its CO. Potato Dave has suggested to
me (cone 6 guy) to use wollastonite rather than whiting for CaO
sourcing. Just cut back on your silica and tada? maybe? [scratches
armpit] Banana?
Taylor "what-does-he-know" Hendrix, in Waco
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Mud Duck
Pottery
Sent: Wednesday, February 11, 2004 4:49 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: ash blisters
Help!!!
I have been experimenting with the following glaze.
Cone 6 ox.
Wood Ash (mostly oak) 50 (un washed)
Gertsley Borate 20
Whiting 12
Epk 8
Silica 10
Rutile 2
Cobalt Carb. 1.5
This glaze is beautiful but I get these random blisters. When the
blisters
are broken open there's a little honeycomb under the blister.
I spray the glaze on the bare bisque pot, with no other glaze
underneath.
I bisque to cone 07 and fire to cone 6 with a 20 minute soak at the end.
I
have a computer control on my kiln (L&L) and have noticed that cone 6 is
only firing to 2193 F. and on the cone charts cone 6 is 2232 F.
So what I'm wondering is should I fire this glaze to cone 7?? Will this
get
rid of the blisters or should I look for something else that might be
the
problem??
I have tried other ash glazes and get these #$^^#@_)(*(& blisters with
all
of them.
...
Mud Duck Pottery on wed 11 feb 04
Help!!!
I have been experimenting with the following glaze.
Cone 6 ox.
Wood Ash (mostly oak) 50 (un washed)
Gertsley Borate 20
Whiting 12
Epk 8
Silica 10
Rutile 2
Cobalt Carb. 1.5
This glaze is beautiful but I get these random blisters. When the blisters
are broken open there's a little honeycomb under the blister.
I spray the glaze on the bare bisque pot, with no other glaze underneath.
I bisque to cone 07 and fire to cone 6 with a 20 minute soak at the end. I
have a computer control on my kiln (L&L) and have noticed that cone 6 is
only firing to 2193 F. and on the cone charts cone 6 is 2232 F.
So what I'm wondering is should I fire this glaze to cone 7?? Will this get
rid of the blisters or should I look for something else that might be the
problem??
I have tried other ash glazes and get these #$^^#@_)(*(& blisters with all
of them.
Gene Arnold
mudduck@advi.net
John Britt on thu 12 feb 04
If I remember correctly Gerstley Borate, Laguna, Gillispie, Boraq, CC-298
and soda ash all melt around 1550 F. (This is and general estimate.)
Hope that helps,
John Britt
Ivor and Olive Lewis on thu 12 feb 04
Dear Gene Arnold,
First thing to do is to account for the blisters. Then you can think
of creating a cure.
You might consider that your Gerstly Borate is melting and sealing the
surface before all of the Whiting has completed decomposing and
evolving gas. Give that as a possible cause and you would need to slow
down the ramp rate just above 850=BA C. and hope that gas evolution was
completed before your Gerstly Borate and the Soda or Potash carbonates
of your ash totally melted.
By the way, does anyone have a melting point figure of GB or any of
the other replacement compounds.
Best regards,
Ivor Lewis. Redhill, South Australia
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