Craig Martell on sun 17 sep 00
Hi:
The main reason Gerstley Borate provided some good suspension properties in
glazes was due to the bentonite content of the material. It's been stated
and documented that Gerstley Borate was actually Ulexite and this mineral
was associated with bentonite in the US Borax mine. So, if other boron
minerals are used, or frits, and you don't get the pudding effect, you can
add bentonite or the smectite of your choice to restore some particle
flotation.
I wrote some posts a while back about working on some blue celadons and one
of them had no clay in the recipe. This can cause severe settling. I
tried a couple of things. I added about 2% Hectabrite, which is the brand
name for a hectorite material. Macaloid is made of hectorite ore. This
helped a bit but I still had to stir the glaze at 10 minute intervals. The
colorant I use for the blue celadons is black iron oxide which can cause
some spots and is a bit hard to disperse without a lot of screening so I
ball milled the next batch for 1 hour. The suspension is greatly improved
due to a more homogenized grind of the whole batch and the iron is well
dispersed and I don't have spots in the finished pieces. Anyway, I liked
the Hectabrite. It's easy to use and mixes well into the glazes and
suspends most very well. It's made by US Colloids I think.
later, Craig Martell in Oregon
Martin Howard on mon 18 sep 00
I have no problems with glaze suspension using standard Borate Frit with cat
litter. The montmorrillinite, bentonite, in the dried and recycled cat
litter works fine, up to 20 percent of total.
There are other borate frits available, and other additions which we can all
experiment with, so the loss of one individual product need not, IMHO, cause
anyone particular problems.
What seems to be essential, for so many contributors to this wonderful list,
is to get a good glaze program, have your RMs tested, put them into the
program, substitute within the program and then test, test, test.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
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