Joan Carcia’s Terra Sigillata Recipe

On Monday, we brought you Joan Carcia’s saggar-firing technique. Today, as promised, we’ll share the other secret to her success with this technique: her terra sigillata recipe. Enjoy! – Jennifer Harnetty, editor.


This recipe (see ingredients below) makes about 1 cup of white terra sigillata. Mix it in a 1-gallon container with a lid. Mix the trisodium phosphate into the water, then add the clay slowly over a period of 1520 minutes, letting each addition slake down before adding more. After all the clay has been added, let it sit for about half an hour, then vigorously mix with a spatula for about two minutes. Then put the lid on the jar and shake it vigorously for another two or three minutes. Next, place it in a spot where it will not get moved for two weeks.


After two weeks, siphon off the clear water on top. Then, using a turkey baster, siphon the next layer (terra sigillata) and put it into a jar for using. Throw out the sediment that is left at the bottom. The terra sigillata should be like skim milk in consistency. If it is too thick, you can add a little water.



I apply this terra sigillata to bone-dry pots with a soft brush, overlapping my strokes. I put two or three coats on and burnish the pot either after each coat or after the final coat with a soft cloth. It is important to stir the terra sigillata mixture to keep it in suspension during application. I bisque my pots to Cone 08 before firing in the gas kiln.

More images of Joan Carcia’s work can be seen at

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