Frank Gaydos on tue 8 may 07
Any thoughts on why suddenly our cone 04 oxidation glazes are crawling =
away from each other during the electric firing and falling off the pot =
when one glaze is placed upon another?
In the past we had no problems.
The only difference I can see is I am using either bentonite or epsom =
salts to keep the low fire glazes in suspension.
Do you think either one or both are causing the problem?
Frank
Linda Arbuckle on wed 9 may 07
This could be off-base, but we had a shop glaze that was crawling when
thick, leaving glaze on the kiln shelf. It was high in Gerstley borate and
clay, and if it got on thick (beginning students, often, or double-dips -
with high clay and g.b. it was easy to get on thick) it often cracked in
drying - sometimes very visible if really thick, or sometimes not so evident
raw - and either fell off the piece during firing and/or crawled. I
re-formulated to reduce the clay and g.b. - using some frit - and it seems
to be working better, less fussy to apply. Too much bentonite could also
cause similar issues, I think. Pete Pinnell had a good article on crawling
problems in Clay Times July/Aug 2004, that I found illuminating.
If anyone wants the glaze details:
Old glaze that behaved badly raw
Faux lead strontium base cone 04( makes iron ambers and grass greens
w/copper)
Frit 3110 30.6
Gerstley borate 33
EPK 26
Flint 5
Wollastonite 3
Strontium carbonate 2.5
Amber + 5-7% burnt umber
grass green transp + 4% copper carb
re-formulated (and re-named by glaze lab assistant who did the testing for
us):
Amber Assault cone 03
Frit 3134 60
Wollastonite 2
Strontium carbonate 3
Kaolin 21
Flint 1
Kona F-4 feldspar 14
5% burnt umber for amber. 4% copper carb for green transparent
Linda Arbuckle - Univ of FL Ceramics
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