|Monthly Tech-Tip |
Being fired at cone 04, this talc body is quite porous. Water is entering through the unglazed base. During an overnight immersion it penetrated upward to about 1 cm from the rim (and even travelled two-thirds of the way up the handle). So, is this clay and temperature practical for functional ware? Yes. The base can be glazed or siliconed, completely stopping water entry. Heating this in the microwave for an extended period did not fracture it. And even though the mug got incredibly hot the G3879 glaze did not craze - that gives reasonable assurance it will hold up over time. Low-fire bodies have plenty of advantages and they are certainly practical for functional use. Additionally, handmade items deserve common sense care during use (e.g. not leaving pieces in water for extended periods, even hand washing).
The bases of many artware pieces can actually be glazed and then fired on the kiln shelf without using stilts. How? A thin layer of silica sand and a super thin layer of clear glaze on the bottom - just thick enough for the melt to soak in a little and seal the body against water penetration (of course the side walls are the regular three coats). How thick? Just experiment. In this example, I watered down some Spectrum 700 clear and applied one quick coat. It does not seem like enough but it produces a glassy surface that picks up very few grains of silica sand during firing. In the worst case, when applied too thickly, some grains of sand will stick, but even then they can be rubbed off and the piece is still ok.
Clay Body Porosity
In ceramics, porosity is considered an indication of density, and therefore strength and durability. Porosity is measured by the weight increase when boiled in water.
Microwave safety is a concern in the production of function ceramic ware.
G3879 - Cone 04 Transparent Low-Expansion transparent glaze
A super transparent low fire base clear glaze created by reverse engineering a commercial product.