Ceramic Materials

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Formula: 2CaO.3B2O3.5H2O or CaB3O4(OH)3·H2O

Oxide Weight160.49
Formula Weight205.49
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.
DENS - Density (Specific Gravity) 2.95
HMOH - Hardness (Moh) 4.5
GSPT - Softening Point 1050C
SLBY - Solubility in HCl but not in water

Colemanite has been a popular natural source of insoluble boron for many decades. It is similar to Ulexite in its oxide contribution to glazes (although the latter sources Na2O also). Frits are used as boron sources in industry whereas potters and smaller companies have used colemanite.

Colemanite does not melt as low or as uniformly as Ulexite. Gerstley Borate contained significant amounts of colemanite. Pure colemanite, however, is much higher in B2O3 than Gerstley Borate.

Colemanite is available from Turkey, Chile and California. The chemistry of these varies quite a bit, and of course, none of the available materials have the theoretical chemistry shown here.

Very high percentages of colemanite in a glaze can result in wrinkling of the fired surface, likely due to to a phenomenon called 'decrepitation' that occurs when colemanite is heated. Be sure to screen out any materials coarser than 200 mesh, or ball mill the glaze. Gum or other binders also help.

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In Bound Links

By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Colemanite" descrip="" searchkey="" loi="0.00" casnumber="1318-33-8"> <oxides> <oxide symbol="CaO" name="Calcium Oxide, Calcia" status="" percent="27.300" tolerance=""/> <oxide symbol="B2O3" name="Boric Oxide" status="" percent="50.800" tolerance=""/> </oxides> <volatiles> <volatile symbol="LOI" name="Loss on Ignition" percent="21.900" tolerance=""/> </volatiles> </material>

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