Figures made from oil-based clay.
While the types of skills and techniques used to shape and form modeling clay into works of art remain largely consistent for any type of clay, the different formulas and types of clay you use make a big difference in what you can do with the finished product. Natural mineral and man-made modeling clays have different properties, formulas and techniques for use that make each kind best suited for certain types of use, ranging from home crafts to teaching to fine ceramics.
Air-Dry Earthenware Clay
These clays are water-based and will dry to hardness when exposed to air. Besides water, they contain fine mineral particles. This type of clay is great for creating permanent art projects, but the resulting, hardened product will melt if exposed to water. You can counteract this and make your project water-resistant using a coat of sealant, but this will not make the clay waterproof enough for outdoor decorations or dishes that will contain food or drink.
Kiln-Fired Clays
Kiln-fired clays are a mineral clay that, after air-drying, can be fired in a kiln to create a permanent ceramic. This happens because the heat causes both chemical and physical changes, fusing the mineral particles permanently. Some firing clays fuse at low temperatures for a rough, earthy ceramic, while others, fused at higher temperatures, create a glass-like ceramic commonly known as porcelain.
Polymer Clay
Polymer clay is a man-made modeling product designed to harden in a conventional oven. Polymer clay is made from the same kinds of plastic agents found in PVC pipe and contains no natural mineral clay particles. This type of clay is popular for craft projects, especially figurines and jewelry, but due to it's chemical nature is not to be used for any object meant to come into contact with food.
Oil-Based Modeling Clay
Originally invented in the late 1800s and given the brand name "Plasticine," oil-based modeling clay was invented for the sake of art creations designed to stay soft. This allows sculptors time to create objects with a high degree of complexity. It is most commonly used for pedagogical purposes and for clay model stop-motion animation ("Claymation").
Specialty Clays
A number of additional specialty craft modeling products are made and sold, usually designed around the concept of mixing a powder of a recycled material with water to create a molding dough. These can include paper clay, children's flour-based modeling dough and metal clays (designed to be fired into real precious metal products).
