This very fine slip is made by creating a slurry out of the clay, then adding a large amount of water and a deflocculant (such as a modern water softener). The deflocculant helps keep the finest particles in suspension, while larger particles settle to the bottom. After two to three days, the cloudy top half to three-quarters of the jar is siphoned off. The particles are dropped out of suspension by adding a flocculant, such as Epsom salts or vinegar. The clear water is siphoned off, leaving a small amount of terra sigillata slip.
Once created, the slip was applied very thinly and then burnished. After firing the ware was sealed using oil, animal fat, or wax. This sealing process acts to both protect the fragile pots and to decrease their absorption of water or other liquids.
Potters today usually use terra sigillata in conjunction with burnishing, just as in ancient times. Many also use smoking, sawdust firing, and metallic salts to increase the visual interest of the pot's surface.
There are a number of contemporary potters working with terra sigillata in conjunction with smooth forms and smoky firing methods. (noun)
Creating terra sigillata slip takes patience. (adjective)