|Monthly Tech-Tip |
Straight-sided thin walled slip cast porcelain pieces are very prone to warping. To assure the rim fires perfectly round a fool-proof solution is to fire them upside down on a refractory setter having a ridge that matches the inside diameter of the fired rim (upper right).
On the left you are looking at four objects for 3D printing, each has 0.8mm thick walls (my printer extrudes 0.4mm wide). The bottom shows the inner cup itself visible through the partially transparent outer shell mold. I fill the cup with plaster, extract it, polish and soap the plaster surface and stick it upside down to a smooth surface (using a sticky ball clay slurry). Then I stick the outer 3D printed shell down around the cup form and pour in plaster to make a working mold. Sure enough, thin walled cups cast in that mold all warp when fired to vitrification. By averaging the inside minimum and maximum rim diameters I get the measurement needed to create the setter press mold top left (of course I must factor in the total shrinkage of the refractory L4482B). By pouring plaster into that I get press molds for making the setters.
A ceramic whose priorities are translucency, whiteness, fired strength and resistance to thermal shock failure.