I want this engobe to gel in ten seconds. Why?

Friday 25th September 2015

It is going to be applied to leather hard earthenware and it needs to be thixotropic (gelled when not in motion, liquid when in motion). Why? I do not want it to run down from the rims of the mugs after dipping. The process: Stir the engobe, pour-fill the mug, pour it out and push it upside down into the engobe. If I can pull it back out before the 10 second gel-time is up I get a perfectly even layer that does not move. A good test is to stir it then pull out the spatula slowly. If it hangs on in a even layer with only a few drips it is perfect. Achieving this behaviour requires very careful additions of powdered epsom salts (and thorough mixing between). As the slip approaches this 10 second threshold even a slight bit more salts will turn it into a bucket of jelly (if that happens I add a drop or two of Darvan). This process works across a range of specific gravities (about 1.45-1.6), the higher the SG the trickier it is (but the faster it dries).

Pages that reference this post in the Digitalfire Reference Database:

Engobe, Terra cotta, Thixotropy

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