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Soda Feldspar

Formula: Na2O.Al2O3.6SiO2
Alternate Names: Na-Feldspar, Na Feldspar, Albite

OxideAnalysisFormula
Na2O11.82%1.000
Al2O319.44%1.000
SiO268.74%5.999
Oxide Weight524.53
Formula Weight524.53
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) 2.60
MLRG - Melting Range (C) 1100-1150C

Soda Feldspar is generally a clean white mineral that sources sodium, alumina and silica along with some potassium and calcium. No actual materials have the ideal formula shown here, they all have some K2O and small amounts of other contaminants. Manufacturers refer to their materials as 'soda' if Na2O predominates over K2O (often manufacturers refer to their materials at soda-potash feldspars (or vice versa) if neither of the oxides predominates). Nepheline Syenite is often used in similar circumstances, however it has a higher alumina content (often the lower alumina content of soda feldspar provides more room in glaze recipes for alumina sourcing ball clay or kaolin to help suspend the slurry).

Albite mineral, from which soda feldspar is derived, often tends to be white in appearance compared with the pinkish hue of orthoclase mineral from which potash feldspar is ground.

In many cases soda and potash feldspar are interchangeable in glaze recipes. However, some differences will be apparent. Soda feldspar normally melts better. Also, slightly different color responses will be encountered (i.e. cobalt tends toward purple copper toward blue with soda spar). Sometimes colors will be brighter with soda feldspar. In addition, soda spar has a higher coefficient of expansion and melts earlier and has a shorter range before it begins to volatilize.

Crazing Alert:
Because sodium has the highest expansion of all oxides and because it is high in this material, glazes with a lot of soda spar will almost always craze. Thus, if any glaze recipe has more than 30% soda feldspar, it is wise to test carefully to assure the glaze is not in tension (use glaze calculation software to reduce the Na2O and replace it with CaO, MgO or another fluxing oxide if possible). It is important to remember that if a glaze is high in Na2O, diluting it with other oxides to try to reduce crazing is a losing battle, it is the cause of the problem, it needs to be reduced.


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Pictures
A comparative flow test of Custer, G-200 and high soda and high potassium feldspars from i-minerals.com

Click for 543% larger


By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Soda Feldspar" descrip="" searchkey="Na-Feldspar, Na Feldspar, Albite" loi="0.00" casnumber="12168-80-8"> <oxides> <oxide symbol="Na2O" name="Sodium Oxide, Soda" status="U" percent="11.820" tolerance=""/> <oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="19.440" tolerance=""/> <oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="68.740" tolerance=""/> </oxides> </material>


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