GERSTLEY BORATE: Replacing It in Your Glazes

much boric oxide in a glaze recipe calling
for x units of colemanite one needs to use
15x and adjust the clay and whiting con-
lent downward in some recipes”.

In 1996, Laguna cited this composition
(ex-US Borax):

B203 28% (</- 3%)

MaZO 5.3%

CaO 20.6%

Water of crystallizavion 25.0%

Moisture (average) 0.3%

Insoluble minerals (limestone,
dolomite, clay, others) (8.7%

1992 A nalysts/Formula from Laguna Clay
3102 9.8%
Al203 1.3%
NalO 4.7%
K20 0.14%
CaD 17.9%
MgO 3.5%
Fe203 0.35%
B203 283%
*H20 & CO2 IGN LOSS 29.1%
*ASSUMED INERTS.... 4.9%

Novice that GB is about 4)% boron and
30% volatiles. [fF you fire a powdered sam-
ple to cone O10 you will find that it weighs
VO less.

Back to Replacing Gerstley Borate
in Glazes

Glazes can be viewed as mixtures of ce-
ramic minerals and manufactured ceramic
powders. However each of these materials
melts in the kiln and contributes its chem-
istry to the overall chemistry of the glare.
This overall chemistry determines the
glazes fired properties. Boron, or B203, is
an oxide, # partol the chemistry of Gerstley
Borate. [tis alow melting glass, when itis
Dlended with other oxides like S102,
Al203, CaQ, etc. you get a ceramic glaze
that melts well at lower temperatures, The
real advantage of looking al a glaze as a
collection of oxides is that reducing and
increasing individual oxides has much
more predictable effects than manipulat-
ing the amounts of materials in the recipe.

See next month's newsletter for the can-
tinuation of this article.

Related Websites
Way crramicsearch.com/oanide/

http: //digalfire.com

Help to Convert Glaze Recipes
Ron Roy <ronroy @ astral. magic.ca>

The information in this article has been
Prepared by Tony Hensen with the
#enenerous support of Plainsan Clays
Limited. Ifyou have queries, please call or
email the editor or the Guild office,

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