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The unglazed surface of the left piece has a sheen, it is a product of glass development during firing to cone 6. That body is a 50:50 mix of a cone 8 stoneware and a low fire earthenware red (a material that would normally be melted by this temperature). Together they produce this dense, almost zero-porosity ceramic. The unglazed surface on the right looks more like plaster, and it is absorbent, about 5% porosity. It is a mix of the same stoneware but with 50% ball clay. The refractory ball clay assures that the stoneware, which was already inadequately vitreous, is even more so. As you can imagine, the left piece is far stronger.
Glossary |
Fired Strength
Ceramics, by their brittle nature, have high compressive strength. But in functional ceramics we are more concerned about the tensile strength as this relates better to serviceability. |
Glossary |
Restaurant Ware
If you are a potter and want to make restaurant ware, read this. Many of the things you already think you know will mislead you in this type of venture. |
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. |
Glossary |
Vitrification
A process that happens in a kiln, the heat and atmosphere mature and develop the clay body until it reaches a density sufficient to impart the level of strength and durability required for the intended purpose. Most often this state is reached near zero p |
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