Left: Plainsman M340 fired to cone 6 where it achieves about 1.5% porosity, good density and strength. Right: H550, a Plainsman body intended to mature at cone 10, but fired to cone 6 using the same glaze. Although the glaze melts well and the mug appears OK, it is not. It is porous and weak. In fact, it has cracked during use (the crack runs diagonally down from the rim). It was then dipped into water for a few moments and immediately the water penetrated the crack and began to soak into the body (you can see it spreading out from the crack). If this glaze were to craze the entire thing would be waterlogged in minutes.
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.
A term used in ceramic to express the degree to which an item is safe and stands up to everyday use. Functionality embodies strength, hardness, resistance to acid attack and thermal shock, etc.
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