|Monthly Tech-Tip |
These are commercial bottled glazes, a transparent and a decorative. On a porcelain at cone 6. They are not compatible with the body (its thermal expansion is too low or they are too high). This not only creates a germ zoo but severely weakens the piece. I tapped this lightly with a spoon about 1-2 cm below the rim. It sounded like I was hitting a wet sack of rocks! And after the first tap the handle fell off! With each tap the pitch dropped. The piece breaks apart the same way auto-glass does in a collision. This type of functional ware is entirely unacceptable. If you use commercial glazes test their compatibility with the bodies you use. If you make your glazes, adjust their recipes to reduce the thermal expansion until no crazing occurs using a thermal stress test (e.g. the IWCT test, which anyone can do). If buy ware like this return it for a refund.
Crazed ceramic glazes have a network of cracks. Understanding the causes is the most practical way to solve it. 95% of the time the solution is to adjust the thermal expansion of the glaze.