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cracked cups

updated wed 27 may 09

 

Brenda Phillips on tue 26 may 09


I was stunned to have a friend call to say that one of my cups was =3D
leaking coffee!
I made it with icelia clay, fired to cone 6, glazed with the bone glaze =
=3D
(MC6G) on the inside and weathered bronze on the outside. The crack =3D
encircles the cup (not completely, thank goodness) about 2/3 of the way =3D
up. I looked up cracks in Hamer's dictionary and it resembles the Crack =
=3D
F for glazed ware. I think that my design is the problem due to =3D
thickness variation. 7/16 " to 3/8" within 1/2". That variation caused =
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too much stress. It was just recently fired but I didn't notice a crack =
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and didn't test it with boiling water. =3D20
Does it make sense that it is the thickness variation that would cause =3D
the cracks?
I'm hoping that you all agree that that is the cause since it is easy to =
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correct. =3D20
Thanks,
Brenda from Manchester, CA