|Monthly Tech-Tip |
A broken section of dried paper clay (a kaolin-only porcelain). This contains 1% by weight paper fiber. Notice the fibers at the break, these give it great strength in the green state. At 1% there is a significant effect on the working properties of the plastic material. It is much tougher, resistant to tearing. But it is harder to achieve a smooth surface. 1% is likely the most paper you would want to put in a body for common use.
This measuring cup contains 30 squares of toilet paper or 11 grams (which has disintegrated quickly and has been propeller-mixed). I am about to dump the paper fiber and 1000 grams of plastic porcelain powder into the water and then mix that up and pour the slurry onto a plaster bat. Although the fiber is only 1% by weight of the dry mix, this completely changes the working properties of the clay. It is still plastic, but much more difficult to cut with a knife or wire. It rolls out nicely into very thin slabs and they are very tough and easy to manipulate and build with. As it hardens it is still pretty plastic.When forced to bend it slowly breaks as the fibers release across the boundaries. Two dry pieces of this clay can be joined using only water and they stick together! Of course this paper needs to burn out during firing, so you need good ventilation on your kiln. You might think that this paper clay shrinks much less than the non-paper version. Actually, it shrinks more (likely because of the increased percentage of water needed). The paper is imparting strength, that strength is enough to resist cracking on drying.
In ceramics, drying performance is very important to optimizing production. More plastic clays shrink more and crack more, but they are also better to work with.