Terra Sigillata is a very refined slip, that is, clay in suspension, applied to unfired clay pots to get a smooth finish that is not glaze, although it mimics a satin glaze for its durability and water-proof properties. It is usually used in low fire applications like saggar, pit fire, horsehair and burnished carved works. I have been experimenting taking it to cone 6 (about 2250 F degrees) on my more functional pieces.

I have always loved the look of unglazed clay but the feel of it is sometimes reminiscent of fingernails on a chalkboard. These few pieces that I have made so far are promising, and I certainly enjoy the process.

To make the Terra Sigillata, into my special bucket, I mix clay and water with an addition of sodium silicate, which allows the clay to “unclump” and mix thoroughly in the water. I let this mixture sit undisturbed for about a day. Then, I open the top spigot to let off the excess water, then open the bottom spigot to drain off the part that I want, and discard what is left.