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Potash Feldspar

Alternate Names: K-Feldspar, Orthoclase, K Feldspar, Potassium Feldspar

Oxide Analysis Formula
K2O 16.92% 1.00
Al2O3 18.32% 1.00
SiO2 64.76% 6.00
Oxide Weight 556.74
Formula Weight 556.74


One of the most important materials for medium and high temperature ceramic glazes. Potash feldspars are often not as pure and white as soda spars. A feldspar is typically referred to as 'potash' if there is significantly more potassium than sodium (typically there will be 2-5% Na2O). If the amounts are closer to equal they are termed potash-soda feldspars (or vice versa). Of course, real potash feldspars also have small amounts of CaO, MgO, Fe2O3, etc.

Potassium feldspar melts at around 1200C (higher than soda feldspar) producing a more a viscous melt than does sodium feldspar. It can also produce a crystalline phase (leucite) that contributes to opacity. Thus, in industry, potash feldspars are often used more for matte glazes while soda feldspar is used for glossy glazes.

Glazes high in feldspar (35% or more) are plagued by crazing problems, yet still used by tens of thousands of potters. 'Flux saturated' glazes with more than 50% feldspar may be unbalanced and lack adequate glass former or alumina to create a stable hard glass resistant to leaching.

Related Information

Orthoclase Crystals

Orthoclase In Granodiorite

Orthoclase Feldspar Rock


Materials Cornwall Stone
Materials Soda Feldspar
Materials Custer Feldspar
The most common potash feldspar used in ceramics in North America. While having been a standard for many decades its supply appears in doubt in 2024.
Materials Feldspar
In ceramics, feldspars are used in glazes and clay bodies. They vitrify stonewares and porcelains. They supply KNaO flux to glazes to help them melt.
Materials Calcium Feldspar
Materials FK45 Feldspar
Materials FM6 Feldspar
Materials KM71 Feldspar
Materials 261-F Feldspar
Materials SP-G Feldspar
Materials Clinchfield #202
Materials Sil-o-spar
Materials Keystone Feldspar
Materials NC-4 Feldspar
Materials MC Na-200 Feldspar
Materials Maine Feldspar
Materials Elbrook Feldspar
Materials Madoc Feldspar
Materials Yankee Feldspar
Materials G-40 Feldspar
Materials G-200 Feldspar
Materials G-20 Feldspar
Materials F-20 Feldspar
Materials A-3 Feldspar
Materials Eureka Feldspar
Materials Mahavir Potash Feldspar
Hazards Feldspar
Feldspars are abundant and varied in nature. They contain small amounts of quartz (while nepheline syenite does not).
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Feldspar
The most common source of fluxes for high and medium temperature glazes and bodies.
Typecodes Materials used in Denmark
Oxides K2O - Potassium Oxide
Minerals Microcline, Anorthoclase
A potassium feldspar.
Minerals Sanidine
A potash feldspar mineral.
Minerals Anorthosite
A plagioclase feldspar rock containing ilmenite.
Minerals Leucite
Hardness: 5.5-6 Density: 2.5 K2O 21.50%, Al2O3 23.50%, SiO2 55% An alumino-silicate common to gr


Frit Softening Point 1250C M
Frit Softening Point 1200-1250C M
Density (Specific Gravity) 2.56
By Tony Hansen
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