kaolin, hydrated alumina silicate, pure clay material
location: Magnet Cove, AR

use in ceramics: Kaolin can be used as a clay body, but in order for it to be plastic enough to handle and fire to maturity and not crack, it needs to be mixed with other materials like frits, bentonites and ball clays. Many porcelains only contain a kaolin mix as their clay component. In glazes, kaolin is used to keep silica, feldspar, frit, and other particles from separating. When fired in a glaze, kaolin contributes alumina (aluminum oxide) to the chemistry of the glaze which acts as a stabilizer.

use in paints: Calcined kaolin, which is kaolin that has been fired between 500-800 degrees Celsius, is used as an extender for titanium dioxide (white) pigment. This is because kaolin clay is chemically inert, has a high covering power, gives desirable flow properties and reduces the amount of expensive pigments required. Its hardness also improves physical durability of the paint film and its burnish resistance. Kaolin clay is also used in grounds, which are applied to a surface to prepare it for paint. The ground dries quickly and several very thin layers applied one after another to form a ground typical of 19th century paintings.