Linda Arbuckle on sat 14 sep 96
Naridel,
This may not really help, but....
I had problems with my majolica glaze having random matt patches on the
glaze surface, especially the white areas without colorant and flux painted
on top. The glaze seemed uniformly thick all over, so it wasn't thinness.
In the end, after tearing my hair, I read in Harry Fraser's book "Ceramics
Faults and Their Remedies" ( a great book!) that I probably had a "bitty"
glaze. Over time slightly soluble ingredients in the glaze (usually calcium
compounds ,as I recall) form insoluble crystals. These ended up on the
surface of the pot, and usually were where ever the glaze ran last in
dipping. Eg. if I dipped a cup and held it rim down as I pulled it out of
the bucket, the matt spotts were near the rim; if I pulled the cup out of
the bucket and turned it rim up right away, the matt patches were near the
bottom.
Harry said to screen that stuff! He recommended a 120 or 150 mesh screen.
Sure enough. Since I have long work periods between glazing sessions, I
screen my glaze before using it, and it's cured the roving matt spots. I
have about 8 gallons of majolica glaze mixed up for dipping (5% tin, which
may just be co-incidence), and usually just top up the bucket w/a new batch.
This and the fact that my studio has been unheated/cooled until recently
aggravated the problem, I suspect. When winter came and the glaze cooled
(this is north Florida, so it's unlikely to actually freeze, altho the air
temp. may go down to freezing for a couple hours at night in winter), it
probably forced materials out of solution.
Since your problem seemed to be just toward the elements, this may not be
your solution. (no pun intended)
Linda
_______________________________________________
Linda Arbuckle E-mail: ARBUCK@nervm.nerdc.ufl.edu
Associate Professor, Graduate Co-Ordinator
Univeristy of Florida
Department of Art P.O. Box 115801
Gainesville, FL 32611-5801 Ceramics: (352) 392-0228
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