|Monthly Tech-Tip |
This is made from 100% of a natural clay (3B) from the Whitemud formation in Ravenscrag, Saskatchewan. I rolled the plastic clay into a thin layer, cut it into a cross-shape, drape-molded it over a plaster form and then slip-joined the seams. It fires very dense and strong (to zero porosity like glass!). It holds together well and joins well with its own slip. Although not super plastic, it is smooth and fine-grained like a commercial porcelain body. I add 1-2% bentonite to make it more plastic when needed. It has the ability to be rolled extremely thin and yet does not warp in the firing! This mug has a weight-to-volume ratio of 2.08 (the weight of water it will hold compared to its own weight).
Not so fast! Cone 10R ware is only strong if the glaze fits. Fortunately this does. But either one will break if dropped on the floor. The stoneware clay has a porosity of 2.5-3%, the earthenware 12%. But the entire base of the orange one is glazed (it was fired on a three-pointed stilt), and the glaze fits well, so there is no point-of-entry for water. The stoneware mug has bare clay exposed on the foot so it will absorb some water. The stoneware mug weighs 432g, the other 281g. It holds only 1.16 times its weight in water, the orange one 1.92! The earthenware is a much better thrower. It is also a much better insulator, you can hold your hand around it with scalding hot coffee inside. And only two pint jars and a brush were needed to glaze it. And it fired in four hours. I needed to make two pails of glaze for the other and took 22 hours to fire! My favourite to use right now: The orange one.
These four sections were glued together to make a larger one. Now it is possible to quickly precision-cut the shape for making my pie-crust mugs. Later I re-printed these templates on a better 3D printer so the inner vertex holes cut out much better.
Mother Nature's Porcelain - Plainsman 3B
Pie-Crust Mug-Making Method
Tony Hansen's project to make light, strong and functional slab-built mugs using tools and templates made possible by 3D design and 3D printing.
How to Find and Test Your Own Native Clays
Some of the key tests needed to really understand what a clay is and what it can be used for can be done with inexpensive equipment and simple procedures. These practical tests can give you a better picture than a data sheet full of numbers.