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Boraq 2

Oxide Analysis Formula
CaO 25.40% 0.76
K2O 0.50% 0.01
MgO 3.60% 0.15
Na2O 3.20% 0.09
B2O3 26.50% 0.64
Al2O3 2.40% 0.04
SiO2 11.90% 0.33
Fe2O3 0.10% 0.00
Oxide Weight 122.87
Formula Weight 166.94


Boraq 2 is a Gerstley Borate substitute that was made by Plainsman Clays. It was derived from Boraq 1 in response to these issues:

-The boron levels in Boraq 1 were deliberately higher than Gerstley Borate so that it would melt as well at low temperatures (GB has tramp minerals that no material made from more pure minerals will have). That meant that Boraq 1 was melting too much at cone 6.

-The MgO in Boraq 1 was also lower than GB (it contains very fine MgO-rich clay particles that source the plasticity, the Hectalite addition in Boraq 1 was not sufficient to supply it all).

-Boraq 1 was not working well with iron reds at cone 6. It seemed evident that this was because of either the lack of CaO or the lack of limestone-like minerals that occur in Gerstley Borate.

Boraq 2 adds 8 dolomite and 8 calcium carbonate to Boraq 1. The dolomite supplies the needed MgO. Gerstley Borate is basically calcium-borate, so adding the calcium carbonate dilutes the boron.

The chemistry of Boraq 2, Boraq vs Gerstley Borate (mole%):
Boraq 2 Boraq 1 GB
CaO 34.7 29.1 30.4
MgO 8.0 5.4 7.6
KNaO 4.6 4.8 5.7
B2O3 34.3 38.9 33.8
Al2O3 1.6 1.8 0.9
SiO2 17.2 19.5 21.6

While no longer manufactured, the process by which it was developed is over interest to technicians.

Related Information


Materials Boraq
Materials Boraq 3
Materials Gerstley Borate
Typecodes Flux Source
Materials that source Na2O, K2O, Li2O, CaO, MgO and other fluxes but are not feldspars or frits. Remember that materials can be flux sources but also perform many other roles. For example, talc is a flux in high temperature glazes, but a matting agent in low temperatures ones. It can also be a flux, a filler and an expansion increaser in bodies.
Recipes P5283 - Boraq 2 Recipe

By Tony Hansen

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