Ceramics of indigenous peoples of the Americas
The clay body is a necessary component of pottery. Clay must be mined and purified in an often laborious process, and certain tribes have ceremonial protocols to gathering clay. Different tribes have different processes for processing clay, which can include drying in the sun, soaking in water for days, and repeatedly running through a screen or sieve. Acoma and other Pueblo pottery traditionally pound dry clay into a powder and then remove impurities by hand, then running the dry powder through a screen, mixing it with a dry temper, and then mixing water to create a plastic paste. In preparing the clay, potters spend hours wedging it to remove air pockets and humidity that could easily cause it to explode during firing. The clay then needs to "cure" over time.
Ancient Egyptian pottery
The marl clay (or 'desert clay') is found along the Nile valley, from Esna to Cairo, in the Oases and at the edges of the Nile Delta. It is a yellow-white stone, which is found in limestone deposits. The deposits were created in the Pleistocene, when the original Nile river and its tributaries deposited this clay in what had previously been desert. Marl clay includes a range of kinds of clay based on their base substance. In general, they have a lower percentage of silicum and significantly higher calcium content. The most important sub-types of marl clay are:Marl clay is normally cream or white in colour when it is fired in an oxygen-rich oven. Cuts can reveal pink or orange areas. It is rich in mineral salts, so the outer surface often has a thin layer of weathered salt which forms a white surface layer when fired, which can be mistake for a 'glaze' by the unwary. At higher firing temperature (c. 1000 °C), this layer becomes olive-green and resembles a green glaze.