Pottery is formed while clay is in its plastic form. Either a long piece of clay is coiled and then smoothed, or the clay is centered upon a potter's wheel (used in Egypt before 4000 B.C.) that spins the clay while it is being shaped by the hand, or thrown. Decoration may be incised, and the piece is allowed to dry to a state of leather hardness before firing it in a kiln. The type of finish, depending on the kind or number of glazes, dictates the total number of firings. When slip and graffito are used, they are applied before the first firing. There are two types of fires—reducing and oxidizing. The former removes oxygen while the latter, a smokeless fire, adds it. Reduction and oxidation change the color of the fired clay and gave early potters their palette of red, buff, and black.