|Monthly Tech-Tip |
These are made from a 50:50 mix of bentonite and ball clay! The drying shrinkage is 14%, more than double that of normal pottery clay. It should be impossible to dry them, the most bentonite bodies can normally tolerate is 5%. Yet notice that the handle joins with the walls are flawless, not even a hairline crack (but the base has cracked a little). Remember that the better the mixing and wedging, the smaller the piece, the thinner the walls, the better the joins, the more even the water content is throughout the piece during the entire drying cycle and the more damp of a climate you live in the better your drying success will be. What did it take to dry these: 1 month under cloth and plastic! I changed the cloth every couple of days. So by implementing these same principles you will have better drying success.
Clay Cracking During Drying
The best way to avoid drying cracks when making ceramics or pottery is to avoid doing the things that cause it. Do not just blame the clay, anything can technically be dried.
Drying Ceramics Without Cracks
Anything ceramic ware can be dried if it is done slowly and evenly enough. To dry faster optimize the body recipe, ware cross section, drying process and develop a good test to rate drying performance.
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.
Clays used in ceramics shrink when they dry because of particle packing that occurs as inter-particle water evaporates. Excessive or uneven shrinkage causes cracks.