|Monthly Tech-Tip |
These bi-body strips are made by rolling two clays together in a thin sandwich. Three porcelains are being compared to a very plastic grogged sculpture body. After drying (top) they curl a little, two toward the sculpture body and one, the most plastic of the porcelains, toward the white. But on firing to cone 8 they curl dramatically toward the porcelain side (because it shrinks alot more). Now imagine one of these porcelains is being used as a engobe on this body.
In ceramics, clays with added aggregate are free formed or molding into shapes that are slowly dried and fired in a kiln. The process requires much skill.
Engobes are high-clay slurries that are applied to leather hard or dry ceramics. They fire opaque and are used for functional or decorative purposes. They are formulated to match the firing shrinkage and thermal expansion of the body.
During drying, clay particles draw together and shrinkage occurs. During firing the matrix densifies and shrinkage continues. More vitreous bodies shrink more.