An excessively high temperature of the mixture causes its vitrifaction and loss of its permeability to air, which prevents this circulation of air. |
So, I don't know if you know the vitrifaction test for clay. |
It is during vitrifaction, however, that the secret formulas and the skilled hand of the artist are decisive. |
The vitrifaction or vitrified fraction of the instant invention is made conventionally in a smelter or the like. |