Tom Buck on tue 4 feb 97
Michael Redwine: After I sent a reply to you yesteday, a nagging doubt
entered, and I went back to source. Namely, Pp 143-147 of Carlton Ball's
"Pottery without a wheel" vintage early 1970s.
For C5 Oxidation potters, Ball developed some excellent glazes
that still circulate today. His MC 532A Turquoise C5 Ox was listed as
follows:
600 Barium Carbonate
1350 Nepheline syenite
140 Ball clay
160 Flint
70 Copper carbonate
70 Lithium carbonate
And he notes: "This is a heavenly copper blue mat."
If one uses Strontium carbonate instead of BaCO3, one would use
450 grams of SrCO3, and as a result the proportions of the other
components shift a bit relative to the SrO in the recipes Seger formula.
I had said the glaze had a lead-bearing component; I mistook the
Turquoise one for the BC DRY MATT next on the page in which is used white
lead.
BTW Ball notes in a preamble: "These glaze should work well from
cones 4 to 6, depending on the firing of the kiln and how you prefer your
glazs finished." Ball could well have added, the actual result will vary
with a given C5/6 claybody.
Cheers TomB Hamilton ON Canada URL http://digitalfire.com/magic/tombuck.htm
Sandra Dwiggins on wed 5 feb 97
The variation with the clay body is really quite minimal. As I mentioned in
a previous post, I used this quite a lot before the barium problem became
known, with several different clay bodies, some with lots of iron, some
with little iron, etc. The differences were not that apparent. However, it
is a very open textured surface, and absorbs any food that
manufactures any liquid--therefore, it changes color and stains. Unless
the strontium changes the surface texture, this glaze is not
recommended for often-used functional ware.
Sandy
Robert S. Bruch on thu 6 feb 97
Tom Buck mentioned that "one ould use 450 grams
of strontium (SrCO3) ......." to replace the
600 grams of Barium Carb (BaCO3).
I had thought that the Barium/Strontium replacement
ratio was .75 Barium = 1.00 Strontium, and not the
other way around.
Anyone know the correct ratio?
--
Bob Bruch rsb8@po.cwru.edu
Richard Burkett on fri 7 feb 97
Bob Bruch asks:
>I had thought that the Barium/Strontium replacement
>ratio was .75 Barium = 1.00 Strontium, and not the
>other way around.
No, it is the other way around.
The usual replacement is a 1:1 molecular substitution - one atom of
strontium for every atom of barium. This gives a 0.75 strontium carbonate
for every 1.00 of barium carbonate replacement ratio by weight (grams,
ounces, pounds, tons, whatever).
Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/index.html
| |
|
