|Monthly Tech-Tip |
The foot ring on these hard mugs has already been trimmed. At the stiff-leather-hard stage an engobe was applied to the inside. This rewet the bodies of the mugs, almost to the same point as freshly-thrown. But the handles did not get rewetted. To re-dry these mugs to the point of being able to turn them over will take 4-6 more hours. But by that time the handles will be bone dry. To prevent that I waxed them after trimming. That slows their drying down enough to keep them even with the body of the mug. To dry ware successfully the key is to keep all parts of a piece of the same water content throughout the process.
In ceramics, drying performance is very important to optimizing production. More plastic clays shrink more and crack more, but they are also better to work with.
Engobes are high-clay slurries that are applied to leather hard or dry ceramics and fire opaque. They are used for functional or decorative purposes.
During drying clays and porcelains shrink as they become rigid. When this occurs unevenly, cracks are the result.
L3954B - White Cone 6 Engobe Recipe
Dry and firing shrinkage fitted to Plainsman M390, M340