|Monthly Tech-Tip |
Alternate Names: K-Feldspar, Orthoclase, K Feldspar, Potassium Feldspar
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.
Orthoclase In Granodiorite
|Oxides||K2O - Potassium Oxide|
The most common source of fluxes for high and medium temperature glazes and bodies.
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.
Materials used in Denmark
|Materials||Mahavir Potash Feldspar|
|Materials||MC Na-200 Feldspar|
|Frit Softening Point||1250C M|
|Frit Softening Point||1200-1250C M|
|Density (Specific Gravity)||2.56|