Classes and Types of Clay
Earthenware clay was one of the first clays ever used by potters. In today’s pottery world it has become one of the most commonly used clays due to the wide variety of colors within the class. The colors that can be found in Earthenware are brown, red, orange, medium grey, and white. This particular clay contains high amounts of iron and a number of mineral impurities, making it one of the easiest clays for potters to work with.
Stoneware is a plastic clay that reaches its maximum hardness between 2200-2336 degrees Fahrenheit. The original colors of Stoneware is light grey or buff and turns to a neutral grey color when the clay becomes even the slightest bit moistened.
Ball clay is a dark grey, highly plastic clay that contains very few mineral impurities. Although this particular class of clay increases plasticity when added to another type of clay, it cannot be used alone due to excessive shrinking during the firing process. Ball clay is commonly used to make a porcelain mixture with Kaolin or with Stoneware clays to make a unique finished look.
Although fire clays are mostly clear of all mineral impurities, they obtain specks of iron which results in a speckled appearance after the clay is fired. Fire clays not only used for pottery, but also used to create cone packs that help to seal doors.
Kaolin (Porcelain) Clays
Kaolin is mainly used for porcelain because of its mineral purity. Kaolin comes only in light colors and are only slightly plastic, making the clay extremely difficult to work with. Because of the difficulty that comes from working with Kaolin, it is mixed with Ball clay to create the perfect porcelain mixture. Out of all classes of clay, Kaolin has the highest temperature maturity levels with Fahrenheit degrees as high as 3272 F.
Types of Clay
Here is a video of David Gibson explaining the different types of clay you might come across: