Mix dry materials with water and then slowly add the sodium silicate. Blunge thoroughly using a propeller mixer and set aside for 24 hours. The next day you should notice three distinct layers. Siphon off the middle layer into a separate container. This is your terra sigillata. It should feel very creamy and smooth. Discard or add remaining clay material to reclaim.
This is a good white base that you can add stains to. I typically add 1–2 tablespoons of Mason stain per 2 cups of terra sigillata.
This recipe was shared by Jeffrey Lipton in the November 2023 issue of Ceramics Monthly.