Ceramic Oxides

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K2O (Potassium Oxide)

COLE - Co-efficient of Linear Expansion 0.331
GSPT - Softening Point 707C (From The Oxide Handbook)


-Together with sodium and lithium oxides, it is classified as one of the Alkaline group. Colored glazes whose flux portion is alkaline-dominated tend to be visually intense, especially if the alumina is low.

-K2O is considered together with sodium, since the two almost always occur together and have very similar properties. When taken together the two are often labeled KNaO. K2O generally promotes higher melt viscosity than Na2O.

-It is an important auxiliary flux in high temperature glazes.

-It is a heavy oxide and in general hosts the brightest colors of all fluxes except for lead. It is usually preferred even to soda for a more brilliant glossy glaze and longer firing range. Very good colored glazes can be made in K2O-PbO-SiO2 dominant formulas.

-Considered a very stable and predictable oxide.

-Like sodium, it has a very high expansion, this tends to contribute to crazing in higher amounts, but not quite as bad as sodium. Thus high alkali glazes almost always craze. If the color depends on this (i.e. copper blue), then it may be necessary to adjust the body to eliminate crazing (since a reduction of the alkalis to reduce crazing will mean a loss of color).

-The alkalis can increase lead solubility.


  • Glaze Color - Pink

    Alkaline glazes with barium and small amounts of Mn can produce pink.

  • Glaze Color - Tenmoku

    Reduction tenmoku black-rust glazes with 8-10% iron work well in high potash glazes.

  • Glaze Color - Blue

    0.5-1.0% iron in potassium reduction glazes may give delicate blue to blue green.

  • Glaze Color - Copper Red

    Copper red reduction glazes are best in formulations with high alkali. The presence of boron can give a more pleasant red.

  • Glaze Color - Copper Blue

    Oxidation copper blues work best in high alkaline, low alumina glazes. Increasing copper to 4-6% will move color toward turquoise.

  • Glaze Color - Cobalt Blue

    Cobalt blues can be very intense in alkali glazes (up to 2% cobalt).

  • Glaze Color - Violet

    Alkaline dominant glazes will produce violet, purple, burgundy, red blue using manganese dioxide to 2%.

Out Bound Links

  • (Materials - Material source) Cornwall Stone

    Cornish Stone, China Stone, Corn Stn, China-stone

  • (Materials - Material source) Potash Feldspar - K2O.Al2O3.6SiO2

    K-Feldspar, Orthoclase, K Feldspar, Potassium Feldspar

  • (Materials - Material source) Nepheline Syenite - Generic

    Neph Sy

  • (Materials - Material source) Frit - Frit master

    Ceramic Frits

  • (Materials - Closest material equivalent) Pearl Ash Calcined - K2O - Pure source of K2O

    Potash Calcined, Calcined Potash

  • (Materials - Material source) Pearl Ash - K2CO3

    Potassium Carbonate, K2CO3, Pearlash

  • (Materials - Material source) Sylvite - Soluble source of K2O

    Potassium chloride, KCL, Silvin, Silvine

In Bound Links

  • (Glossary) Alkali

    Alkalies are the strong base fluxing oxides of Na2...

  • (Oxides - Substitute) Na2O - Sodium Oxide, Soda
  • (Minerals) Feldspar

    An indispensable material in the ceramic industry....

  • (Minerals) K-Feldspar

    Most common feldspars contain both sodium and pota...

By Tony Hansen

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