Air-hardening modelling clays allow you to create permanent, hardened works of clay art without the need for ovens or kilns. These water-based clays are convenient and inexpensive to work with, but the material can present a few challenges, both practical and artistic.
Prepare for a mess. Most air-dry clays are made up of water and pasty materials that tend to leave thick residue on your hands, tools and work surface. This mess washes away with water, but it's best to keep it away from clothes and porous surfaces. Lay down newspaper or use a smooth table and wash it afterward. Wear old clothes or an apron and be prepared to not to be able to use your hands for anything else while you're working with the clay.
Keep a bowl of water on hand. Air-hardening clay often partially dries out while you're working with it and you need a little water worked into the clay on a regular basis while you're sculpting. If you have a large bowl of water, you can also use it to keep your hands and tools a little cleaner while you're working.
Condition the clay before you start working with it. Pull as much clay as you think you'll need for your project and knead it in your hands, adding a little water as you go if the clay is crumbly or lumpy rather than smooth. This both softens the clay and distributes the moisture evenly throughout, giving it a consistent texture. Keep working with and moistening the clay until it's soft, but not pasty.
Prepare for shrinkage. Air-hardening clay hardens because the water inside it evaporates. When this happens, the mass of the clay reduces and the finished sculpture will be slightly smaller than it was when it was wet. Clay manufacturers strive to create formulas with the least shrinkage possible, but there's always going to be a small size reduction, usually 25 per cent or less.
Attend to the sculpture while it's drying. Avoid mould growth while the clay is drying by keeping it in a dry area or drying it in a warm oven (65.5 to 93.3 degrees C). Turn the project upside down or on its side to allow the bottom of the clay to dry after the top has finished drying.
Coat the finished clay project with a layer of sealant. After the clay hardens, it is not waterproof, but you can make it resistant to moisture by adding a coat of clay sealant, craft sealant or any varnish or polyurethane coat. This will not make the project fully waterproof or able to hold water or food, but it will protect it from moisture in the air or light contact with water.