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

Notes

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

Links

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

Data

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

By Tony Hansen
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