May 2026: We are continuing a major code rewrite. Please contact us if you find issues. Thank you.
The cone 6 glaze is well developed; it is not crazed. But the clay underneath is not vitreous. This crack happened when the mug was bumped. It is barely visible. But when the mug was filled with water, this happened. How fast? This picture was taken about 5 seconds later. If this were crazing, and this piece was in actual use, the clay would become completely waterlogged. Then one day, someone would put it in the microwave. Boom!
This being said, if the glaze never crazes, the foot ring is sealed and the piece never cracks, this mug could service for years.
| 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 |
Microwave Safe
Microwave safety is a concern in the production of function ceramic ware. |
| 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. |
![]() PayPal | No tracking, No ads, No paywall, No transient content! Just organized, concise information constantly updated and improved. Was this helpful? Consider supporting me. |
Buy me a coffee and we can talk