Modeling clay is a term that covers a group of malleable products used for sculpting and building by children, art students, hobbyists, and professionals including potters and animators. All types can be shaped and worked with tools for sculpting, blending, texturing, thinning, scraping, poking, and cutting. They can also be rolled with rolling pins or in pasta makers, molded, and worked with tools such as extruders, potato mashers, and garlic presses to create various effects. Modeling clay can be built up on its own or built onto a pre-formed armature. There are four basic types of this material.
Oil-based modeling clay, sometimes called plastilina or even plasticine, a name genericized from a trademarked term, was invented in Germany by Franz Kolb in the 1880s and independently by William Harbutt in England in 1897. This material has several distinct properties that make it useful: unlike pottery clay and wax, it stays soft and workable; it neither hardens nor dries. Unlike pottery clay, it comes in a wide array of colors that can be used as purchased or blended. Also, unlike pottery clay, oil-based modeling clay doesn’t stick to your hands. It cannot be fired, however.
Polymer modeling clay is available as several products under the names of Fimo®, Sculpey®, and Premo®, for example. These different materials have various degrees of softness at room temperature, and they can be mixed to combine their individual properties — for example, to make a softer clay stiffer by combining it with a firmer clay. They are finished by baking in an oven at 265°–275°F (129°–135°C) for 15 minutes for each ¼ inch (6mm) of thickness.
Although they are made to be paintable upon baking, polymer modeling clays are available in a wide variety of colors, which can be mixed. In addition, some special feature colors have been created, including translucent, fluorescent, metallic, and bright colors. Other featured specialty clays have a stone texture or glow in the dark.
Dough modeling clay, which may be edible or inedible, resembles the product PlayDoh®, and is often, in fact, called playdough. Playdoughs are easily made at home in both cooked and uncooked versions, and are less expensive than some of the other types of clay. They are made of such ingredients as flour, cornstarch, cream of tartar, oil, and water. They can be colored when made, for example, with food coloring, or have color added after.
One of the useful features of dough modeling clay is that it reusable, though, for example, in the case of a gingerbread house, baking is used to set and preserve the form. Flour-based products — including PlayDoh®, which clearly states that it is meant to be used and reused rather than employed to make lasting items — have a tendency to crack as they dry. However, there are some other types of air-drying modeling clay available, sometimes called “curable clay,” such as Activ-Clay® and Model Magic®, that yield better results in this respect.
Pottery or Firing Clay. This material is used for pottery and stoneware, and is worked by hand and on a potter’s wheel. It is meant to be air-dried and then fired in a kiln. Glazes with glossy, matte, or specialty finishes are used to decorate pottery and are baked on during the firing process. There are low fire, mid, and high fire clays, and glazes for each type.
Pottery clay is usually available in terra cotta, a rust-colored clay, and white, which may appear gray when moist, but dries white. However, some clays do have different tints. Clays are described by their raw and firing color; texture; amenity to throwing, slab, and other particular uses; and the size(s) and thickness(es) for which they work best.