That’s because this Roman tableware often had names or decorations stamped onto them.
Today, the name is used for clay slip made from iron-rich river clay, which is applied to leather-hard clay. Once this slip layer has been polished, the terra sigillata gets its characteristic shine. You can achieve different colours and shades depending on the clay powder you start with.
When making terra sigillata, the finer clay particles are separated from the larger ones. The heavier particles sink down faster than the lighter, fine particles, so they form a separate layer. It is the layer of fine clay particles on top that is used to create the typical, softly shiny effect.
