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Left: Plainsman M340 fired to cone 6 where it achieves good density (about 2% porosity) and excellent strength. Fire it to 1% porosity and it will bloat and warp. So cone 6 is its practical optimal temperature. Being able to measure the 2% porosity demonstrates water penetration, albeit slow penetration. So glazes must fit to seal the surface.
Right: H550, a Plainsman body intended to mature at cone 10, but fired to cone 6 using the same glaze. The clay is much more porous. The piece was dropped and cracked (the crack runs diagonally down from the rim). It was then dipped into water for a few moments. Immediately the water penetrated and began to soak into the body (spreading out from the crack). If this glaze were to craze, the entire thing would be waterlogged in minutes. But it doesn’t craze. So, the piece would be usable (with a sealed foot ring of course).
| Glossary |
Functional
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. |
| Glossary |
Glaze fit
In ceramics, glaze fit refers to the thermal expansion compatibility between glaze and clay body. When the fit is not good the glaze forms a crack pattern or flakes off on contours. |
| Glossary |
Maturity
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. |
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