In order to contain liquids in containers in the ground, we must cover it a glassy coating, called “glaze”. It is a kind of glass layer, composed of silica and lead oxide: silicon substance not only to 1700 °, temperature too high for land that supports it, by adding lead oxide it lowers the melting temperature of the glaze between 800 ° and 1 000 °.

It can affect the color of the land, which turn red when they contain iron oxide, or white when they contain limestone, silica, kaolin, in this case, the two superimposed layers of earth color different, and it widens again to the lower. Read More…

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