B2O3 is a low melting glass


By adding B2O3 to the glaze, you can have it melt at almost any common kiln temperature you want and get a brilliant finish that won't crack. Na2O melts as well or better than B2O3, but unlike B2O3, its high thermal expansion limits it to a lower percentage.

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Boron oxide is colorless translucent glass block or white hard odorless crystal. Melting point 450 °C; bp: 1860 °C. Density: 2.46 g cm-3. Slightly soluble in water. Used as an insecticide; as a starting material for the synthesis of other boron compounds; as a flux for enamel and glass; mixed with 2-6% boron nitride, as a binder for hot isostatic pressing boron nitride ceramics.

Diboron trioxide is a type of boron oxide with the molecular formula B2O3.

B2O3 is a low melting glass with low thermal expansion and low surface tension. It is a very useful oxide that is indispensable in many industries and applications. By adding B2O3 to the glaze, you can have it melt at almost any common kiln temperature you want and get a brilliant finish that won't crack. Na2O melts as well or better than B2O3, but unlike B2O3, its high thermal expansion limits it to a lower percentage.

 

Below cone 10, the addition of B2O3 is almost always required to fully melt the glaze. Other fluxes, such as ZnO, will melt the glaze at cone 6, but a number of issues limit them to certain types of glazes. The lower you go, the more boron is needed. A melt flow checker is the best way to determine if the glaze has melted enough (and not too much). In cone 06, typically 0.5 mole parts of B2O3 are required, while in cone 6, only about 0.1 to 0.2 are required. Reactive glazes usually contain more boron (eg 0.4-0.5 in cone 6) and these formulations have run problems and lead to various defects. Almost all frits for low and medium temperatures contain boron as their melting mechanism.

 You cannot add powdered B2O3 to glazes, there is no such insoluble substance. It has to be done using glaze chemistry. There are a number of videos showing how to do this using your account on Insight-live.com and Digitalfire Insight. Check out the link to my youtube channel provided here.

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