How stop dripping and running: Add water! Then make it thixotropic.

Friday 15th August 2014

The white slip on the left, L3685Z2, (applied to a leather hard cup) is dripping downward from the rim (even though it was held upside down for a couple of minutes!). Yet that slurry was very viscous with a 1.48 specific gravity. Why? Because it was not insight-live.com/glossary/91">thixotropic. The fix? I watered it down to 1.46 (making it runny) and added pinches of powdered Epsom salts (while mixing vigorously) until it thickened enough to stop motion in about 1-2 seconds on mixer shut-off. But that stop-motion is followed by a bounce-back. That is the thixotropy. It is easy to overdo the Epsom salts (gelling it too much), I add a drop or two of Darvan to rethin it if needed. When the engobe is right, it gels after about 10 seconds of sitting, so I can stir it, dip and extract the mug, shake to drain it and then it gels and holds in place. Keep in mind, this is a pottery project. In industry, they deflocculate engobes to reduce water content and then impose thixotropy, but that is more technical than the average potter would want.

Pages that reference this post in the Digitalfire Reference Library:

Epsom Salts, Creating a Non-Glaze Ceramic Slip or Engobe, Here is what dipping engobes can do: Go on even. In one coat. Stay put., Thixotropy, Rheology, Engobe, Uneven Glaze Coverage

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.