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peeling underglaze

updated thu 10 jul 03


quesuave@OVERLAND.NET on wed 9 jul 03

I have used the same clay and underglazes for many many years with no
problems, but in the last year, some of the underglaze colors have started
to chip off. I first paint the underglazes on greenware, then fire the
piece to a cone 06. Then I put a watered down wash of underglaze over the
bisqued piece and fire again to cone 04. I can see the washed color
underneath the chipping underglaze, so it must start the peeling away
during the first firing. It doesn't happen everytime, and the brands of
underglazes that chip are varied. It happens mostly with Gare and Amaco,
but once in a blue moon Duncan chips, too. I am adding frit to the
underglazes, but don't care for the resulting colors. I have tried adding
APT2, which helps some, but doesn't eliminate the problem. We are using
Armadillo Longhorn clay (which I have used for 20+ years), and used to use
the Grande, but discontinued using it, because it had a lot of grog mixed
in which caused the underglazes to chip all the time. Has anyone out there
had this experience?