Jason F on thu 28 aug 08
Hello everyone:
=20
Relative newcomer here=2C been potting for only a little over a month. I've=
read a lot about what causes cracks during drying and firing=2C but I had =
a question about cracks that form after a piece appears to have successfull=
y fired and has been used:
=20
A friend of mine bought a crystal-glazed porcelain gaiwan--a lidded cup use=
d for Chinese tea preparation--made by Eilong studios in Taiwan (link here:=
http://www.eilong.com.tw/product_tea_china_ware_title_emerald_green_crysta=
l.asp ). After about a week of use=2C the cup cracked apart in a single fra=
cture. I own about a dozen porcelain gaiwan and have not experienced this p=
roblem. Their website indicates the pieces' firing temperature=2C and you c=
an see they intend most of it for teaware=2C where it would be exposed cons=
tantly to boiling water.
=20
What might cause a fracture/breakage like this one=2C and what could I do w=
hen making a piece to prevent it happening?
Many thanks in advance!
--Jason=
Antoinette Badenhorst on thu 28 aug 08
This sounds like a stress fracture and has more to do with the materials used than the technical handling of the clay. The clay and glaze does not fit each other or the clay contains too much silica. There is a slight possibility that it cooled down to fast in the kiln, but I think the breakage would have appeared earlier in such case.
--
Antoinette Badenhorst
www.clayandcanvas.com
www.studiopottery.co.uk
-------------- Original message ----------------------
From: Jason F
> Hello everyone:
>
> Relative newcomer here, been potting for only a little over a month. I've read a
> lot about what causes cracks during drying and firing, but I had a question
> about cracks that form after a piece appears to have successfully fired and has
> been used:
>
> A friend of mine bought a crystal-glazed porcelain gaiwan--a lidded cup used for
> Chinese tea preparation--made by Eilong studios in Taiwan (link here:
> http://www.eilong.com.tw/product_tea_china_ware_title_emerald_green_crystal.asp
> ). After about a week of use, the cup cracked apart in a single fracture. I own
> about a dozen porcelain gaiwan and have not experienced this problem. Their
> website indicates the pieces' firing temperature, and you can see they intend
> most of it for teaware, where it would be exposed constantly to boiling water.
>
> What might cause a fracture/breakage like this one, and what could I do when
> making a piece to prevent it happening?
> Many thanks in advance!
--Jason
The Fuzzy Chef on thu 28 aug 08
Jason,
> What might cause a fracture/breakage like this one, and what could I do when making a piece to prevent it happening?
> Many thanks in advance!
Sounds like thermal shock to me. Probably your friend's cup had a
hidden flaw, and use caused it to split.
--Josh
Ric Swenson on fri 29 aug 08
Possibly the piece was subjected to a physical shock....hit against another piece, dropped or some sharp strike against the sink...or??. The piece looked okay, but then, when subjected to thermal shock, it broke.
Porcelain will usually ring when lightly tapped with a spoon. If it 'thuds' or 'clanks' ...ie. does not ring, there may be a break somewhere that is almost invisible to the eye.
My 2 RMB.
Regards,
Ric
-----------------------------------------------
> Relative newcomer here, been potting for only a little over a month. I've read a lot about what causes cracks during drying and firing, but I had a question about cracks that form after a piece appears to have successfully fired and has been used:> > A friend of mine bought a crystal-glazed porcelain gaiwan--a lidded cup used for Chinese tea preparation--made by Eilong studios in Taiwan (link here: http://www.eilong.com.tw/product_tea_china_ware_title_emerald_green_crystal.asp ). After about a week of use, the cup cracked apart in a single fracture. I own about a dozen porcelain gaiwan and have not experienced this problem. Their website indicates the pieces' firing temperature, and you can see they intend most of it for teaware, where it would be exposed constantly to boiling water.> > What might cause a fracture/breakage like this one, and what could I do when making a piece to prevent it happening?> Many thanks in advance!> --Jason
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