Color, density, size and hardness all change as the firing temperature progresses. The color, for example, persists in zones, then changes suddenly. Notice that the colour of the grog particles contrasts more as the temperature increases. This body is completely vitrified at cone 10 and the grog is important for fired stability.
A term used in the ceramics industry to signify the degree of vitrification in a fired clay. Mature clays are dense and strong, immature ones porous and weak.