The Clay Body
Clay is basically earth. Specifically, it is sedimentary rock made up of silicate minerals with sheet-shaped chemical structures that provide plasticity in the right conditions. Deposits of clay are formed through prolonged erosion of larger pieces of material. Ancient native potters used locally abundant clays to shape basic pottery forms. The clay was "mined," pulverized by grinding and mixed with water to a workable consistency. Then the clay was formed into a pot by using one of two basic methods: hand-coiling or paddle-and-anvil.
In the hand-coil method, wet clay was hand-rolled into snakes and the snakes coiled one layer atop another. As the coils piled up they were pinched together, then scraped on the inside and out to smooth the surfaces and remove extra clay. In the paddle-and-anvil method a slab of clay would be laid over something already formed and it would be smoothed to that shape with the paddle. The Hohokam people were the primary users of the paddle-and-anvil method but they also used the hand-coil method to make the upper portions of their pots once they'd removed the "anvil." Most Pueblo and Hopi potters used a basket bottom or a puki as a base to begin their coiling in.
This part of the process is shared in common by virtually all Native American potters. Where elements differ is in the nature of the local clay itself and in how the potter might be intending to decorate the pot. Archaeologists have used mineralogical and chemical testing to analyze the unique and distinctive properties of ancient pottery in order to identify the location where they were made and the age of the ware.
Colors: White, gray, brown, red, orange, black. Color is mainly determined by the amount of iron and/or other minerals present in the soil. Different locations yield clays with distinct characteristics and colors. All aspects of the creation of the pot were made with clay which was easily available. Early Southwest potters often worked with more than one color of clay. Decoration was applied by brushing darker or lighter colors - red, black and white, over the surface. Sometimes designs were painted directly onto the dried formed clay body. At other times a slip, made from a different color of clay, was washed over the entire surface and allowed to dry before the design was applied.
The properties of the local clay determine the nature of a pueblo's pottery. San Ildefonso, Santa Clara and Jemez have clay bodies that are easily polished, carved, painted and scratched. Taos and Picuris have micaceous clay bodies. Jicarilla Apache and Nambe potters are allowed to share those micaceous clay sources. Santa Ana, Santo Domingo, Cochiti, San Felipe and Sandia have red body clays but most potters slip their dried pots with a yellow clay base before painting them. Isleta, Laguna and Acoma have white clays that are usually slipped smooth with white before being decorated with black, red and orange. Hopi and Mata Ortiz have a variety of clays available, some that can be polished and some that are used as slips and paints. Some Navajo potters burnish their pots, fire them, brush them with pine pitch and burnish them again.
In most cases, the final coloring and overall smoothness of the dried clay body is the background on which the decorations are applied.
Sgraffito is an art process that occurs after the pot is fired and the surface color is set. And depending on the depth of any particular scratch, the color of the revealed clay body beneath may be different.