james w. thomas on mon 19 nov 01
I have just had a problem with a load of ^6 stoneware. The pieces are crazing like, well, crazy. We were trying to get a batch of funtional ware ready for an upcoming local festival and evidently I put to much clear on. We applied three coats of underglaze and then bisque fired to ^06. I dipped the pieces instead of brushing. The inside bottom has minute bubbles trapped in the glaze and even where the glaze is thin the pieces are crazing if rubbed hard with a finger. There is a fit problem with the clear but this was a recomended glaze to fit a suppliers clay body. Cracks sure look good on raku but really suck when looking at a whole kiln load of clear crackled coffee mugs, soup bowls, collanders and serving bowls.
Could I lightly sand blast and refire to see if I get anything salvageable or just write off the whole load?
Any help would be appreciated
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John Hesselberth on tue 20 nov 01
Hello James,
This is a tough one and you have my sympathy. I can't think of any real way
out short term. As you point out, you clearly have a clay/glaze fit problem
in spite of what you were told. The difficult part is that since it is a
commercial glaze you don't really know where you are. By that I mean you
know you have to lower the expansion of the glaze, but you don't have any
information about the current glaze's composition and, therefore, its
expansion characteristics. Hopefully Ron Roy will chime in on this one--he
has a lot more experience than I with problems like this. I don't think
sandblasting and refiring will do much. As you point out even the thin
spots are crazed. Also crazing does weaken the clay. Those cracks in the
glaze initiate tiny cracks in the clay body as well. If have developed one
set of weak spots already and refire you are likely to develop another set
of weak spots.
For the future, consider formulating you own glazes so you know what you
have. Then if you run into a problem like this (which will be much less
likely) you will know where you are and where you have to go.
Good luck,
John
on 11/20/01 12:33 AM, james w. thomas at james_w_thomas@HOTMAIL.COM wrote:
> I have just had a problem with a load of ^6 stoneware. The pieces are crazing
> like, well, crazy. We were trying to get a batch of funtional ware ready for
> an upcoming local festival and evidently I put to much clear on. We applied
> three coats of underglaze and then bisque fired to ^06. I dipped the pieces
> instead of brushing. The inside bottom has minute bubbles trapped in the glaze
> and even where the glaze is thin the pieces are crazing if rubbed hard with a
> finger. There is a fit problem with the clear but this was a recomended glaze
> to fit a suppliers clay body. Cracks sure look good on raku but really suck
> when looking at a whole kiln load of clear crackled coffee mugs, soup bowls,
> collanders and serving bowls.
>
> Could I lightly sand blast and refire to see if I get anything salvageable or
> just write off the whole load?
>
> Any help would be appreciated
>
>
> ----------------------------------------------------------------------------
>
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Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Jeremy/Bonnie Hellman on wed 21 nov 01
Hi James,
Some glazes will craze when they are applied too thickly. How thick is =
"too thick"? It's too thick when it crazes. (Sorry about that-- but it's =
really true.)=20
This is true of all my clear glazes, which have to be applied thinner =
than any other glaze I use.=20
Perhaps your glaze was "too thick" when you dipped it. I imagine that =
I'd like to use a glaze with less water (i.e. thicker) if I were =
brushing it on. I only dip my glazes, and have no experience with =
brushing.
I'm not sure if there are very fine craze lines in the same glaze =
applied thinly. You'd have to look at them under a lighted magnifying =
lens.
Anyway, this is just a thought.=20
Bonnie
----- Original Message -----=20
From: james w. thomas=20
To: CLAYART@LSV.CERAMICS.ORG=20
Sent: Tuesday, November 20, 2001 12:33 AM
Subject: Help on crazed cone 6 kiln load
I have just had a problem with a load of ^6 stoneware. The pieces are =
crazing like, well, crazy. We were trying to get a batch of funtional =
ware ready for an upcoming local festival and evidently I put to much =
clear on. We applied three coats of underglaze and then bisque fired to =
^06. I dipped the pieces instead of brushing. The inside bottom has =
minute bubbles trapped in the glaze and even where the glaze is thin the =
pieces are crazing if rubbed hard with a finger. There is a fit problem =
with the clear but this was a recomended glaze to fit a suppliers clay =
body. Cracks sure look good on raku but really suck when looking at a =
whole kiln load of clear crackled coffee mugs, soup bowls, collanders =
and serving bowls.=20
Could I lightly sand blast and refire to see if I get anything =
salvageable or just write off the whole load?=20
Any help would be appreciated=20
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_________________________________________________________________________=
_____ Send postings to clayart@lsv.ceramics.org You may look at the =
archives for the list or change your subscription settings from =
http://www.ceramics.org/clayart/ Moderator of the list is Mel Jacobson =
who may be reached at melpots@pclink.com.=20
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