What is Terra Sigillata?
Terra Sigillata is a suspension of very fine clay particles in water. Usually white in color, terra sigillata is also made with color additions or with colored clays. It is used as a way to create a smooth dense surface on clay. This happens because the clay particles (3 microns or less) pack together so tightly. When polished, the particles reflect light. These qualities make the surface more reactive to smoke and decorations will have sharp distinct boundaries.

To make terra sigillata, a deflocculant is added to a thin slurry of clay and water and mixed. It is then set aside for 24hrs while the coarse particles settle to the bottom. The fine particles remain in suspension and are decanted off. The coarse material is thrown away. A second settling period for the decanted suspension allows even more of the coarse particles to settle. Once again, the fine liquid is separated from the coarse. The fine liquid suspension is Terra Sigillata.

Terra Sigillata is applied to bone dry pots prior to bisque firing usually with a wide brush. The “sig” naturally shines when applied but is often polished with something smooth such as a plastic bag. To make mica infused terra sigillata, we add a specific amount of mica to the terra sigillata. Too much mica will disrupt the characteristic terra sig sheen.