|Water (in parts)||2.00|
|Grolleg Kaolin (in parts)||1.00|
|Sodium Silicate or Darvan 7||0.25|
|Chromium Oxide (in tsp per 1 cup sigillata)||0.25|
|Cobalt Carbonate (in tsp per 1 cup sigillata)||0.25|
Mix 1 part clay to 2 parts water, blend well with drill mixer. Add 0.25–0.5% (of the dry weight of the clay) of a deflocculant (sodium silicate or Darvan 7), then drill mix again. Allow heavier clay (red clay) terra sigillatas to settle for at least 6–8 hours, and lighter clays/ball clays to settle for 24–48 hours. After the mixture has settled into distinct layers, siphon out the middle section of the mixture. This is the terra sigillata. Add colorant per 1 cup mixed terra sigillata.
Note: Terra sigillata does not seal a surface once it is fired and therefore is not safe to use on surfaces that will come in contact with food or beverages. Consider additional glaze applications and liner glazes to create food-safe surfaces.This recipe was shared by Rhonda Willers in the September/October 2020 issue of Pottery Making Illustrated.