Gerstley Borate

Plastic Calcium Borate

Chemistry

CaO	24.000
K2O	0.500
MgO	4.000
Na2O	4.000
B2O3	25.000
Al2O3	2.000
SiO2	14.000
Fe2O3	0.500

Volatiles

LOI

26.000

Miscellaneous

Family: Flux Source
Region: North America
Mined At: Unspecified
Raw Mineral: No
Generic: No

Notes

This was mined in southern California for many years. The mine was closed in 2000 and remained stocks will be depleted in 2-3 years. There is alarm across the ceramic community in North America about the demise of Gerstley Borate because it formed the basis of so many glazes. For the best information on substitutes we have a special website at http://www.gerstleyborate.com. There is a page on the site dedicated to understanding what Gerstley Borate was chemically, physically and mineralogically, it is at http://digitalfire.com/gerstleyborate/description.shtml. Deciding on an average chemistry was a big challenge.

There are a number of materials that have been developed as substitutes, these are outlined at the website and in the SeeAlso links in this record.

Here is a quote from Laguna Feb 2, 2004

Gerstley Borate is no longer being mined, has not been for a number of years now. There are no plans that Laguna is privy to, of US Borax or anyone else, to reopen the mine. There is however a stockpile of crude GB in existence that was mined prior to US Borax shutting down their operation. Laguna has been having GB ground from that stock pile since we became aware of it's existence, a couple of years ago. The estimates for how much is really there have varied widely, but the most recent estimate I have goes like this, " If current levels of usage are maintained, the stock pile will last about 10 more years".

(Richard Willis)

A complex calcium borate (borocalcite) ore comprised typically of 30-34% “colemanite” (as a calcium borate pentahydrate), 26-30% “ulexite” (as a sodium calcium borate), 20% “shale” (as a low-iron clay/feldspar/quartz) , and 20% “limestone” (as a calcium carbonate).
It is often used as is in a formula calling for 2CaO, 3B₂O₃, 5H₂O; but it's typical empirical analysis is commonly CaO, 20.60% [0.68], MgO 3.50% [0.16], Na₂O 5.30% [0.16], B₂O₃ 28.00% [0.75], Al₂O₃ 1.10% [0.02], SiO₂ 9.50% [0.29], Fe
₂O₃ 0.30% [0.00], H₂O 25.30% [0.00].
It is a powerful flux, particularly below 1100ºC, and is often used instead of lead for firings down to 600ºC.

Data

Decomposition Temp:
Decomposition Temp:

URLs

Hamil & Gillespie web site - www.hamgil.com
Dedicated web site - http://digitalfire.com/gerstleyborate/description.shtml

Suppliers

Hammil & Gillespie

Authors

Tony Hansen (Owner)

XML

<?xml version="1.0" encoding="UTF-8"?>
<material name="Gerstley Borate" descrip="Plastic Calcium Borate" generic="0" rawmineral="0" searchkey="Colemanite, Calcium Borate, Borocalcite" loi="0.00">
<families>
<family name="Flux Source"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="U" percent="24.000" tolerance=""/>
<oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="U" percent="4.000" tolerance=""/>
<oxide symbol="K2O" name="Potassium Oxide" status="U" percent="0.500" tolerance=""/>
<oxide symbol="Na2O" name="Sodium Oxide, Soda" status="U" percent="4.000" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="2.000" tolerance=""/>
<oxide symbol="B2O3" name="Boric Oxide" status="" percent="25.000" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="14.000" tolerance=""/>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="0.500" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="26.000" tolerance=""/>
</volatiles>
<references>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
</references>
<suppliers>
<supplier name="Hammil & Gillespie" country="US" url="http://www.hamgil.com" label=""/>
</suppliers>
<notes>
<note>This&nbsp;was mined in southern California for many years. The mine was closed in 2000 and remained stocks will be depleted in 2-3 years. There is alarm across the ceramic community in North America about the demise of Gerstley Borate because it formed the basis of so many glazes. For the best information on substitutes we have a special website at&nbsp;<A href="http://www.gerstleyborate.com/">http://www.gerstleyborate.com</A>. There is a page on the site dedicated to understanding what Gerstley Borate was chemically, physically and mineralogically, it is at <A href="http://digitalfire.com/gerstleyborate/description.shtml">http://digitalfire.com/gerstleyborate/description.shtml</A>. Deciding on an average chemistry was a big challenge.
There are a number of materials that have been developed as substitutes, these are outlined at the website and in the SeeAlso links in this record.

Here is a quote from Laguna Feb 2, 2004
Gerstley Borate is no longer being mined, has not been for a number of years
now. There are no plans that Laguna is privy to, of US Borax or anyone else,
to reopen the mine. There is however a stockpile of crude GB in existence
that was mined prior to US Borax shutting down their operation. Laguna has
been having GB ground from that stock pile since we became aware of it\'s
existence, a couple of years ago. The estimates for how much is really there
have varied widely, but the most recent estimate I have goes like this, " If
current levels of usage are maintained, the stock pile will last about 10
more years".
</note>
<note>A complex calcium borate (borocalcite) ore comprised typically of 30-34% &#147;colemanite&#148; (as a calcium borate pentahydrate), 26-30% &#147;ulexite&#148; (as a sodium calcium borate), 20% &#147;shale&#148; (as a low-iron clay/feldspar/quartz) , and 20% &#147;limestone&#148; (as a calcium carbonate).
It is often used as is in a formula calling for 2CaO, 3B2O3, 5H2O; but it\'s typical empirical analysis is commonly CaO, 20.60% [0.68], MgO 3.50% [0.16], Na2O 5.30% [0.16], B2O3 28.00% [0.75], Al2O3 1.10% [0.02], SiO2 9.50% [0.29], Fe
2O3 0.30% [0.00], H2O 25.30% [0.00].
It is a powerful flux, particularly below 1100&ordm;C, and is often used instead of lead for firings down to 600&ordm;C.

</note>
</notes>
<testdata>
<testitem testname="8" value=""/>
<testitem testname="8" value=""/>
</testdata>
</material>

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