Polymer clays are specifically designed for making homemade crafts. They can be cured, or hardened, by baking in an oven at temperatures lower than what is required by most pottery clays. Professional pottery is typically placed in a kiln using very high heat. Polymer versions, such as the various Sculpey brands of clay, can be placed in the average home oven. As with most clay projects, it is important not to over-bake Sculpey clay, as it can scorch and become brittle. After baking your clay, you may choose to leave it as it is, or add either paint or glaze.
Place your Sculpey clay sculpture in the centre of the heatproof surface you will be using. Pizza stones are ideal for this purpose, as long as they will not be reused for preparing food.
Preheat your oven to 135 degrees Celsius.
Put the clay sculpture and the heatproof platform in the oven, centring them on the middle rack for even heating. Set your timer for 15 minutes. Open the windows to ensure adequate amounts of fresh air in your workspace, as fumes will be released during baking.
Put on your oven gloves and remove the sculpture and tile from the oven. Allow the baked clay to cool. Remove your oven gloves and carefully use a toothpick to test an inconspicuous area to determine if the clay has hardened sufficiently.
Bake the Sculpey clay in the oven an additional minute at a time, if more time is needed. You may do this for up to five extra minutes, for a total baking time not to exceed 20 minutes. Turn off the oven and paint, or glaze your baked clay as desired.
Avoid directly breathing in the fumes of baking polymer clay. When concentrated, they can be toxic. Make sure your immediate area is ventilated. Do not bake polymer clays (such as Sculpey) on metal pans or trays. Never use materials that were once used for clay crafts for food containers or food preparation.