From LouisKatz

Soluble: AlkaliMetals

The Alkali Metals sodium and potassium are similar in so many ways and in so many cases that we often treat them as if they were the same. But just because they are often the same it is smart to not consider them the same in all circumstances. They melt at similar temperature. They melt with silica and alumina at similar temperatures. The chlorides melt at similar temperatures, although Potassium is chloride is lower than sodium chloride and sodium carbonate is lower than potasium carbonate. Selection of the lower melting materials may help with volitalization in low fire "Salt" and "Soda" firing.

Potassium compounds are often much more soluble in water than sodium compounds..

Soaking bisque ware in solutions of these materials causes numerous problems. In case of the chlorides rapid firing can cause explosions of the bisque ware. I don't know why. All of these compounds seem to cause small blisters in the surface of the clay. My assumption is that these materials for a glass layer very early in the firing and the sealted surface does not allow exit of gasses. These gases could be gases given off by carbonates and chlorides including the carbonates of chlorides of the materials themselves, or perhaps carbonates or sulphates in the clay. It also seems possible that the bubbles are also just the product of the air in the pores of the clay expanding with the rise in temperature. The rise from say 1700F (1200˚K) -1800F (1255˚K) but this is only a 4.6% change in volume over 100 degrees. It seems to slow to build up in the clay.

If my calculations are correct 0.1 grams of sodium carbonate will create 117.9106 ml (1.2 cup) of CO2? at 1800˚F.

Both of these alkali metals cause glazes that craze.

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Page last modified on February 14, 2018, at 11:52 PM