Chris Schafale on sat 29 mar 03
I've been wondering -- has anyone using this clay, or the Speckled
Brownstone, been experience more blistering in the last several
months? I'm working with a batch of Brownstone dated 6/12/02
and I can't seem to get rid of the blistering, especially with one
family of glazes, despite variations in firing schedules, firing down
more slowly or more quickly, holding longer or shorter, bisquing
higher and lower, etc.
I've been assuming it is the glaze's fault and it may be, but the
problem is much worse than I experienced a year ago with the
same glazes. The problem gets dramatically worse on refiring, so
there's nothing to be done for those pieces but the hammer. I'm
getting at least a couple of blisters on most pieces and more on
some. The problem seems to be worst on horizontal surfaces; I
presume because the glaze tends to flow and fill them in on vertical
surfaces.
Anyone else having a similar experience? I know I need to do
some tests with a different clay to test this possibility, but just
thought I'd ask.... I'm getting ready to (try to) fill a big order and I'm
dreading all the seconds.
The glaze, by the way, is the very simple 3134 50%, silica 25%,
epk 25%, and variations thereof. Most of the variations have some
cobalt, some iron, at least 4% rutile.
Chris
--
Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh, NC)
www.lightonecandle.com
candle@intrex.net
Gary Lee on sun 30 mar 03
I have been using Speckled Brownstone from Highwater for many years with none
of the problems you are encountering. The only time SB will blister, that I
have seen, is when it is fired over Cone 6. Sometimes even to Cone 7 you
will get some blistering but generally it is at Cone 9 that it really shows
up. If you are sure you are firing a good Cone 6 Ox, then you may be having
a glaze problem though from your recipe I can't see what could be causing a
blister problem. I use at least 400 pounds a week of SB and the worst
problem I have is the water % has changed the last year and shrinkage is more
now. Gary
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