TYPES OF CLAY
This is very pure clay and serves as a standard to compare other clays for glazes. It serves as a source of SiO2 + Al2O3. Kaolin is an important ingredient in high-fire white ware and porcelain. Major deposits are in Southeast U.S. North Carolina - residual type South Carolina, Georgia, Florida (plastic) - sedimentary type, but none can be considered plastic like ball clay.
Similar to kaolin, but the particles were deposited in swampy areas where the organic acids and compounds released from decaying vegetation served to break down the clay particles into even finer sizes than those of sedimentary kaolins. Ball clay inparts plasticity and dry strength, small additions (10%) to a stoneware body can increase throwing qualities. Tennessee and Kentucky - major deposits.
These are, generally, plastic clays that fire in the range of cone 6 to 10. Stoneware clays are found all over. They contain impurities (calcium, felds, iron, etc.) that lower maturing temperature and give color from gray to buff.
These are high-firing clays commonly used for insulating bricks, hard firebrick and kiln furniture. Some are plastic, some aren't. Generally, they contain iron, but seldom do they contain calcium and feldspar. They are found almost anywhere and can be high in Alumina and/or silica.
These are low-firing clays (cone 08 - 02). Earthenware clays normally contain a high percentage of iron which acts as a flux when fired quite fragile and porous 5 to 15%, stoneware would be about 3%. Earthenware cannot be made vitreous because of various fluxes. Earthenware deforms, blisters or bloats when fired above 2100o F. These clays are found all over.
These are clays that naturally contain enough flux that they function as a glaze without further additions. (cone6 to 10). The most common form we use is Albany slip.
With the smallest size particle of any clay known, used in amounts and small as 2% as a plasticizer. Bentonite was formed in prehistoric times from airborne dust of volcanic eruptions (large % of silica). This is found in Western mountain states, the Dakotas, and in several Gulf states.