Secondary Clays and Firings. Low-fire (1,112-2,192 degrees Fahrenheit) clay pottery, such as the terra-cottas found in the Nok culture sites (500 B.C.E.) in what is now Nigeria, came from secondary clays (those containing impurities) that produced reddish, brownish, or even gray colors. These clays were far more widely available to West African potters than were the high-fire (2,192+ degrees Fahrenheit) primary clays, which produced white, light gray, or light pink-colored pottery. Moreover, the secondary clays were more easily molded than the primary. If the clay did not contain enough impurities to keep it from cracking or crumbling during firing, sand, plant fibers, stone grit, or grog (fine broken pieces of unglazed pottery) were added. Pottery finds in West Africa often are in the same place as the iron smiths' high-fire furnaces. It is uncertain whether the two technologies—ceramics and iron...