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IMCO Borate

Oxide Analysis Formula
SiO2 21.10% 0.75
Al2O3 0.40% 0.01
SrO 2.00% 0.04
Fe2O3 0.30% -
K2O 1.40% 0.03
MgO 1.80% 0.10
Na2O 3.00% 0.10
B2O3 24.40% 0.75
CaO 19.20% 0.73
LOI 19.80%n/a
Oxide Weight 156.77
Formula Weight 195.48


A Gerstley Borate substitute made by IMCO clays. As of 2023 it is no longer listed on their website.

In our testing appearance and working properties were similar to Boraq, however it dried a faster on the ware.

We measured an LOI of 20.6, this is lower than GB or Boraq. It melts similar to Boraq in the 06 LOI test, however it is smoother and has a tan coloration (so contains some iron).

Related Information


IMCO information on their mined clays
URLs - The best place for info on Gerstley Borate
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 Laguna 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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