Digitalfire Ceramic Materials Database

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Custer Feldspar

Potash Feldspar

Alternate Names: Custer Spar

Oxide Weight621.98
Formula Weight623.85
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.
SIEV - Sieve Analysis 35-325 Wet
Sp TOT 35M 48M 65M 100M 150M 200M 325M NOTE
1 100         0.3 1.0 8.0  

This is one of the main feldspars used in the ceramic industry in North America, especially in the west. It is used in industries such as abrasives, sanitary ware, floor and wall tile, dinnerware, pottery, and electrical porcelain throughout the United States, Mexico and Canada. This ceramic grade high potash feldspar is available in crude, 200, 325 mesh and chip form.

Jan 2012: We were getting reports of a reduction in the potash content. Traditionally it has been reported as around 10% (as is shown in the chemistry given here, it is from their online data sheet dated 3/23/2005). However, analyses of many specimens over the past ten years (as provided to us by Ron Roy) suggests that around the year 2000 the K2O content dropped to about 7.5 (with no accompanying change in the Na2O). However, a melt flow test from Plainsman Clays using 2012 material demonstrates that melting is the same over the past year, it does not detect this possibly longer term trend. The chemical analysis of a load received in Nov 2013 reports 10.1 K2O, 3.1 Na2O and 0.1 Fe2O3 (which very closely matches their reported numbers).

Users should be vigilant to do sieve analysis testing to spot any iron bearing particles in the plus 100 mesh range.

Out Bound Links

In Bound Links


A comparative flow test of Custer, G-200 and high soda and high potassium feldspars from

Melt flow test comparing Custer Feldspar from Feb/2012 (right) with Mar/2011 (80:20 mix of feldspar:Ferro frit 3134 has been used for a good flow at cone 10).

By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Custer Feldspar" descrip="Potash Feldspar" searchkey="Custer Spar" loi="0.00" casnumber="12168-80-8"> <oxides> <oxide symbol="CaO" name="Calcium Oxide, Calcia" status="U" percent="0.300" tolerance=""/> <oxide symbol="K2O" name="Potassium Oxide" status="U" percent="10.000" tolerance=""/> <oxide symbol="Na2O" name="Sodium Oxide, Soda" status="U" percent="3.000" tolerance=""/> <oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="17.000" tolerance=""/> <oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="69.000" tolerance=""/> <oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="0.150" tolerance=""/> </oxides> <volatiles> <volatile symbol="LOI" name="Loss on Ignition" percent="0.300" tolerance=""/> </volatiles> </material>

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