Gerstley Borate
Plastic Calcium Borate
Alternate Names: Colemanite, Calcium Borate, Borocalcite | Oxide | Analysis | Formula |
| CaO | 19.40% | 0.69 |
| MgO | 3.50% | 0.17 |
| K2O | 0.40% | 0.008 |
| Na2O | 4.00% | 0.13 |
| P2O5 | 0.10% | 0.001 |
| TiO2 | 0.10% | 0.002 |
| Al2O3 | 1.00% | 0.020 |
| B2O3 | 26.80% | 0.77 |
| SiO2 | 14.80% | 0.49 |
| Fe2O3 | 0.40% | 0.005 |
| LOI | 29.50 |
| Oxide Weight | 140.60 | | Formula Weight | 199.43 |
| Enter the formula and formula weight directly into the Insight MDT dialog (since it records materials as formulas).
Enter the analysis into an Insight recipe and enter the LOI using Override Calculated LOI (in the Calc menu). It will calculate the formula. |
This was mined in southern California for many years. The mine was closed in 2000 and remaining stocks were to be depleted in 2-3 years. There was alarm across the ceramic community in North America about the demise of Gerstley Borate because it formed the basis of so many glazes. However now (June 2011), the supplier, Lagunaclay.com, says there is a large supply available. For the best information on substitutes visit gerstleyborate.com. There is a page on the site dedicated to understanding what Gerstley Borate was chemically, physically and mineralogically. There are a number of materials that have been developed as substitutes, these are outlined at the website also.
However the best approach is to finding an alternative is the use of ceramic chemistry on a glaze-by-glaze basis (to substitute other materials). In many cases, it is better to use frits to supply the CaO and B2O3, they are more consistent and reliable and do not flocculate or gel the glaze.
Prior to and during the decade of uncertainty about the future of this material, the supplier did not provide updated chemistry information. We rationalized it (as explained at http://gerstleyborate.com) as 24% CaO, 4% MgO, 0.5% K2O, 4% Na2O, 2% Al2O3, 25% B2O3, 14% SiO2, 0.5% Fe2O3 and 14% 26% LOI. In June 2011 we changed the chemistry provided here to the one provided by Laguna on their website (rounded to 1 decimal). This new chemistry has more B2O3 and less CaO (other oxide amounts are fairly similar).
Out Bound Links
In Bound Links
By Tony Hansen    
XML for Import into INSIGHT
<?xml version="1.0" encoding="UTF-8"?>
<material name="Gerstley Borate" descrip="Plastic Calcium Borate" searchkey="Colemanite, Calcium Borate, Borocalcite" loi="0.00" casnumber="71377-02-1">
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="U" percent="19.400" tolerance=""/>
<oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="U" percent="3.500" tolerance=""/>
<oxide symbol="K2O" name="Potassium Oxide" status="U" percent="0.400" tolerance=""/>
<oxide symbol="Na2O" name="Sodium Oxide, Soda" status="U" percent="4.000" tolerance=""/>
<oxide symbol="P2O5" name="Phosphorus Pentoxide" status="" percent="0.100" tolerance=""/>
<oxide symbol="TiO2" name="Titanium Dioxide, Titania" status="" percent="0.100" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="1.000" tolerance=""/>
<oxide symbol="B2O3" name="Boric Oxide" status="" percent="26.800" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="14.800" tolerance=""/>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="0.400" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="LOI" name="Loss on Ignition" percent="29.500" tolerance=""/>
</volatiles>
</material> | 
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