Richard mahaffey on sat 8 jan 00
hi,
I thought Colemanite went out of favor because the mine closed. I have
used Colemanite and then Gerstley Borate since 1969. Only time I had
trouble with it was in Japan where it spit during the glaze fire. I don't
hold much hope for Colemanite from overseas. Testing will tell however,
as my experience may be isloated.
Rick Mahaffey
Tacoma Comunity College
Tacoma, Washington, USA
Tom Buck on sun 9 jan 00
Rick M:
You are correct: colemanite has been unavailable from USA sources
for at least a decade, probably longer. The deposits were small and soon
petered out.
Colemanite is available from Turkey (a large deposit) but reports
from potters in South Africa and Far East say the stuff is a very bad
actor (too much gypsum in it). Besides it comes to USA in shiploads and is
aimed at the chemical industry market so little or none is available to
potters.
The gerstley borate deposit in California was a very small part of
the huge borax deposit nearby. The grade has been falling steadily so it
is not surprising that US Borax would stop blasting the GB deposit and
stockpile the GB pebble.
There is lots of borax so borate frits will long be available. And
there is a new borate mineral that Craig Martell has described. He says it
is superior to GB and gives consistent results. However, it does cost
more.
Finally, if all else fails, you can adapt your methods to use one
of the borax materials to supply the B2O3 in a glaze. Means you have to
fuss a bit more. Of course, high-fire potters won't worry because B2O3 is
seldom used in glazes fired at 1300 oC.
A prosperous Year 2000 to all. Til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
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