In classical times, black-and red-figured vases were an importantGreek export article, balancing payments resulting from grain import. This was especially true in Athens. The red pigment wus always Fe2U3, and the black Fe304. A carefully chosen clay containing iron, which could be formed by hand with a simple patter's wheel, was used for the vessels. The fired ceramic usually provided the red of the vessels. For the black painting, and for the occasionally used red painting (Intentional Red), a layer of finely elutriated clay was painted on. The vessel was fired between 800 and 900 O C , first under oxidizing conditions, then under reducing, and finally again under oxidizing conditions. From the reproductions of Adam Winter it may be concluded that an illitic clay was used for the black figure painting. During the reductive firing, the painted layer became impervious by sintering owing to the K20 content of the clay. A kaolinitic clay, poorer in K20, served for the red painting. This clay remained porous on reduction and was reoxidized, like the ceramic of the vessel, in the second oxidation. For the terra sigillata of the Romans, the entire surface of the vessel was covered with a clay slip, which, on firing under oxidizing conditions at higher temperatures, gave a hard surface, so that the vessels could be used as table utensils.