petuntse

First, its composition—it is made from petuntse, or porcelain stone, which gives the final ceramic its hardness, and kaolin, which brings plasticity—was a secret, a mystery.

“Together petuntse and kaolin fuse at great heat to create a form of glass that is vitrified: at a molecular level the spaces are filled up with glass, making the vessel non-porous.”

The first successful attempt in Europe to imitate porcelain was made at Florence as early as 1580, under the auspices of Francesco I. de’ Medici, but it was not so hard as that of China; that is to say, it was not composed of kaolin and petuntse, but was a soft paste and translucent, which is one of the principal tests of porcelain.

The kaolin used in making porcelain is much softer than petuntse when dug out of the quarry, yet it is this which, by its mixture with the other, gives strength and firmness to the work.

The lime causes the glaze to melt at a lower temperature than would be necessary for petuntse alone.