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Alternate Names: Boraq 1

Description: Plainsman Plastic Gerstley Borate Substitute

Oxide Analysis Formula
CaO 21.80% 0.76
K2O 0.60% 0.01
MgO 2.30% 0.11
Na2O 3.60% 0.11
B2O3 30.00% 0.85
Al2O3 2.80% 0.05
SiO2 13.50% 0.44
Fe2O3 0.20% -
LOI 25.30%n/a
Oxide Weight 146.64
Formula Weight 196.30


This material was developed by Plainsman Clays as a substitute for Gerstley Borate (under code number L3127E). It was unique in that its development and recipe were openly documented online throughout (it became the inspiration and guide for others). The development effort took place during the early 2000s, the initial period when the demise of Gerstley Borate appeared imminent. Other companies, including Laguna Clays introduced similar products at the time. Later Laguna Clays began processing a last stockpile of the material they found at the mine and interest in substitutes waned. In 2023 the cycle appears set to repeat.

Theoretically, Gerstley Borate is calcium borate. But the real material is more complex, it is actually calcium-magnesium-sodium borate with added quartz and clay. The main mineral sources of these are ulexite, colemanite, calcium carbonate, dolomite and a micro-fine clay (the reason for Gerstley Borate's plasticity). Cadycal was used as a substitute for the colemanite and Hectalite for the clay (the latter because it sources needed MgO).

It was thought that with a reliable analysis of GB a mix of the above materials could be crafted to produce the same chemistry and that it would also have the same melting properties. However this did not prove to be the case, the natural mineralogy of GB supplies the oxides in a form that has a more active melting profile. That meant it was necessary to compromise the chemistry match (using a higher B2O3 content) to get the same melt fluidity at low temperatures. That is what this recipe is.

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 of interest to technicians. The development and recipe of Boraq are well documented on line.

Related Information


Materials Laguna Borate
A Gerstley Borate substitute that was available during the early 2000s.
Materials Murrays Borate
A Gerstley Borate substitute that was available during the early 2000s.
Materials Gillespie Borate
A Gerstley Borate substitute that became available during the early 2000s and is still available in 2023.
Materials IMCO Borate
A Gerstley Borate substitute that was available during the early 2000s.
Materials Boraq 2
Materials Boraq 3
Materials Gerstley Borate
Gerstley Borate was a natural source of boron for ceramic glazes. It was plastic and melted clear at 1750F. Now we need to replace it. How?
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.
Typecodes Gerstley Borate Substitutes
Many development efforts to create Gerstley Borate substitutes took place during the early 2000s (the initial period when the demise of Gerstley Borate appeared imminent). A number of companies, including Laguna Clays itself, produced and sold these for many years. When Laguna secured another stockpile at the mine and began producing the original material again, interest in substitutes gradually waned. However, the sudden dramatic price increase in 2023 appears to have initiated the process again. Gillespie Borate appears to be the only viable and visible substitute now. Thus, the substitutes listed here are mostly no longer made. Other high-boron materials shown are also no longer available. We continue to recommend sourcing B2O3 from frits instead. Please contact us if you have a specific recipe and we can work with you in your Insight-live account to develop a new recipe that both eliminates the GB and improves overall working and firing properties.
Recipes G2826X - Randy's Red Cone 5
A popular Gerstley Borate based iron-red glaze.
URLs - The best place for info on Gerstley Borate
The Development of a Gerstley Borate substitute - Boraq
By Tony Hansen
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