|Monthly Tech-Tip |
This DFAC test for drying performance compares a typical white stoneware body (left) and the same body with 10% added 50-80 mesh molochite grog. The character of the crack changes somewhat, but otherwise there appears to be no improvement. While the grog addition reduces drying shrinkage by 0.5-0.75% it also cuts dry strength (as a result, the crack is jagged, not a clean line). The grog vents water to the surface better, notice the soluble salts do not concentrate as much. Another issue is the jagged edges of the disk, it is more difficult to cut a clean line in the plastic clay.
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.
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.