|Monthly Tech-Tip |
This is the L3798E cone 6 buff-burning stoneware slip (it is 35% KT1-4 ball clay, 25% silica, 12% nepheline, 15% EPK, 13% Redart). This recipe was easy to deflocculate to 1.8 specific gravity and yet it was very thin and runny. It pours nicely and does not gel. The former recipe was using a plastic ball clay and this switches it to a larger particle ball clay intended for casting. Thus the amount of deflocculant needed is less. But we did not reduce it, that's why it is so fluid. While not fluid enough to settle out or have poor draining properties, it is nevertheless, slightly over deflocculated. Although pieces can be extracted from the mold quickly, casting time is longer than it should be (for this one 15 minutes for a 2mm thick wall). Another issue is the inside surface: It should feel soapy and smooth in the leather hard state, but it feels sandy! This underscores the need for controlled flocculation (using less deflocculant) to maintain at a slightly more viscous fluidity so that it has thixotropy.
The deflocculation process is the magic behind the ceramic casting process. It enables you to make a slurry of far lower water content and thus lower shrinkage.