Self-Hardening Clays

Claystone

Boneware

Della Robbia

Self-hardening clays (also known as air-dried, air-hardening or non-firing) do not need to be fired in a kiln, and are generally ceramic clay body formulas with a natural additive, such as cornstarch, to make them harden. They are not meant to replace kiln-fired ceramic clay, cannot be used to produce functional ware, and cannot be left outside exposed to the elements. Pieces made using these clays are items for display only. The material should not be fired in a ceramic kiln under any circumstances. It is porous and cannot hold liquid unless sealed on the inside surface.

After a finished piece has dried and been sealed, it can be decorated for display in a number of interesting ways. You can add bright colors using acrylic, oil, latex, or watercolor paint, or you can achieve mute color effects using wood stain, wax pigmentation applications, or clothes dyes. You can also spray the finished piece with special effect paints obtained from hardware stores.

There are two basic types of self-hardening clay. The first type, Claystone, works like plastilina and is usually used over an armature, an internal support device. The clay material generally contains some type of pulp or cotton fiber filler to reduce shrinkage and thus prevent cracking. (The armature will not give when the clay shrinks due to evaporation of moisture.) Please note, there may be some degree of shrinkage when using a water-base material, so expect minor cracking if the piece is thin and modeled over a solid support. Cracking may also appear at sharp angles and joints. The material over an armature will most likely be fatty or more bulky due to the filler that is incorporated in the formula to reduce shrinkage.

The second type of air-hardening clay, Boneware, is used for solid direct modeling that in essence will be supported by its own bulk. It will contain a natural hardener, but not fiber, to reduce shrinkage and will probably feel and react more like a ceramic clay to the touch and in workability.

There is another type of self-hardening material that can be air-dried or fired in the kitchen oven to give the piece more durability. An example of this material is Della Robbia. This type of material will not replace a kiln-fired ceramic clay that is fired in excess of 2000°F fusing the molecular structure and becoming vitrified and non-porous. Please note, for any self-hardening clay there is no known method to emulate vitrification.

Visit our clay modeling store to view our plastilinas, self-hardening modeling clays, armatures, modeling stands and a wide variety of wood and steel sculpting tools and accessories.