As the name suggests, self-hardening clay, also known as air-drying clay, dries on its own when exposed to air. Self-hardening clay is convenient to use at home when you don't have access to a kiln. Different types of self-hardening clays include air-dry clay, air-dry polymer clay, epoxy clay and claystone. Each type has different properties and materials that vary in the drying time and hardness of the clay.
Store the Clay
Self-hardening clay will dry out with exposure to air, so it is crucial to keep the clay sealed at all times. Keep the clay in the plastic bag it comes in, and store the bag in an airtight container. Store the container in a cool, shady place such as a cellar or a basement. When using clay, take out only the amount you need for the project and put the rest away immediately. If you notice clay in the bag beginning to dry out, mist some water into the bag to add moisture back into the clay.
Choose a Project
While many ceramicists like to be spontaneous with clay and take some time to try different ideas, when working with self-hardening clay, it is best to have a design in mind before beginning. Due to the properties of the clay, it will start drying as soon as it is out of the storage container. If you take too much time experimenting, the clay will begin to dry out, making the clay brittle and unable to be moulded into the desired shape. Therefore, decide what you will make before working with the clay.
Mold the Clay
Mold your clay on a canvas-covered board. This will help keep the moisture in the clay and prevent your project from sticking to the table. While working, keep a bowl of water nearby. Dip your hands in the water often to keep the clay moist. If you notice cracks appearing in your project, try using a sponge to moisten the clay. Rub your finger over the damp clay to smooth out any cracks.
Air Dry the Clay
When you're finished with your clay project, set it on a board to dry. This may be the same board you used while modelling, but be sure to remove any excess clay chunks. If the base of your project is thick, you may want to set it on a wire rack to let the bottom dry evenly. Place the board in a dry place that has high ventilation and air flow. Clay should not be put in direct sunlight, as cracks can develop if the clay dries too fast. If the clay still dries too fast, try putting plastic over your project to help it dry slower.
Finish the Clay
Once the clay is completely dry, it is ready to be finished. Seal the clay with a spray lacquer or dip sealer to keep any toxins inside the clay and protect the piece against chips and breakage. Paint your project with acrylic paints for individual designs and colours. Pieces made from self-hardening clay should be for display only and not used for consumption or left outside.