|Monthly Tech-Tip |
|Co-efficient of Linear Expansion||0.331|
|Frit Softening Point||707C (From The Oxide Handbook)|
|Dry M.O.R. (50% Silica)||398C|
-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.
|Materials||Pearl Ash Calcined|
Fluxes are the reason we can fire clay bodies and glazes in common kilns, they make glazes melt and bodies vitrify at lower temperatures.
In glaze chemistry, the oxide is the basic unit of formulas and analyses. Knowledge of what materials supply an oxide and of how it affects the fired glass or glaze is a key to control.
|Oxides||Na2O - Sodium Oxide, Soda|
|Oxides||KNaO - Potassium/Sodium Oxides|
|Glaze Color||Alkaline glazes with barium and small amounts of Mn can produce pink.|
|Glaze Color||Reduction tenmoku black-rust glazes with 8-10% iron work well in high potash glazes.|
|Glaze Color||0.5-1.0% iron in potassium reduction glazes may give delicate blue to blue green.|
|Glaze Color||Copper red reduction glazes are best in formulations with high alkali. The presence of boron can give a more pleasant red.|
|Glaze Color||Oxidation copper blues work best in high alkaline, low alumina glazes. Increasing copper to 4-6% will move color toward turquoise.|
|Glaze Color||Cobalt blues can be very intense in alkali glazes (up to 2% cobalt).|
|Glaze Color||Alkaline dominant glazes will produce violet, purple, burgundy, red blue using manganese dioxide to 2%.|