|Monthly Tech-Tip |
An example of a highly fluid glaze melt that has pooled in the bottom of a bowl. The fluidity is partly a product of high KNaO, thus it is also crazed (because KNaO has a very high thermal expansion). While it may to decorative, this effect comes at a cost. The crazing weakens the piece, much more than you might think (200%+). Those cracks in that thick layer at the bottom are deep, they want to continue down into the body and will do so at the first opportunity (e.g. sudden temperature change, bump). Also, fluid glazes like these are more likely to leach.
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.
Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it.
Ceramic glazes melt and flow according to their chemistry, particle size and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them.