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Laguna Borate

Description: Gerstley Borate Alternative

Oxide Analysis Formula
CaO 18.90% 0.71
Fe2O3 0.10% -
SiO2 18.70% 0.66
B2O3 27.50% 0.83
Al2O3 8.10% 0.17
Na2O 4.00% 0.14
K2O 1.40% 0.03
MgO 2.30% 0.12
LOI 19.00%n/a
Oxide Weight 171.12
Formula Weight 211.26


Laguna Clay promoted this as a specially formulated flux containing a high percentage of boron, a material that mimicked the fluxing characteristics of Gerstley Borate. As of 2023 this is no longer listed on the website.

Laguna Clay claimed this is almost identical in every glaze they had tried and was less expensive than Gerstley Borate. At first they offered to help users adapt. Early testers posted messages confirming that Laguna has been helpful when they had trouble. Others confirmed that its contribution to fired appearance was very similar for some glazes. In our melt flow tests it looked the same (melting to a clear amber free-flowing glass at cone 06). However, some users reported issues.

Its chemistry was quite different from GB. Iron reds, metallics and floating blues were reported to be different, possibly for this reason. Many glazes in which GB was used contained no clay and thus relied totally on it for suspension, thixotropy and dry hardness. 6-8 parts by weight of bentonite or hectorite were need for for each 100 parts of LB to resolve this. However Laguna chose to source the alumina, silica, and magnesia from sources other than clay so adding clay altered the chemistry of the product. Chrome-tin pinks and reds depend on easily-available CaO (Gerstley Borate contained limestone) - LB testers reported issues with this. Opalescence and variegated surfaces were due in part to the mineralogy of GB, some users commented that these effects are not duplicated with LB.

But here is no question about it, Laguna Borate was the least expensive option.

Related Information


Materials Boraq
This Gerstley Borate substitute was available during the early 2000s. Its recipe and development are well documented but two materials are no longer available.
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.
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.
By Tony Hansen
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