Pottery clay hardens when exposed to the extremely high temperatures of a kiln, which is a specially designed oven that bakes all sides of the pot at the same time. Most clay requires firing in a kiln to harden properly, but with some pottery clay types it's possible to skip the fancy kilns and dry your pieces in your home oven.
Use a polymer clay, which has additives that let you bake it in the oven. Alternatively, make your own clay by combining the flour, table salt, tartar and boiling water. Add a few drops of food colouring to create a coloured clay.
Let the pottery sit out overnight or longer, which helps dry out the piece and make it less green. If you put the piece directly into the oven, you risk breaking or damaging it. Keep the pottery out in the sunlight, which helps it dry faster.
Set the oven to 150 degrees C (350F) and allow it to reach this temperature. Traditional clay pottery requires a high temperature that home ovens can't reach. Handmade clay sets and dries at a much lower temperature.
Place your clay pottery pieces into the oven on a baking tray. Place the baking tray on the middle shelf of the oven and leave it for at least 30 minutes. Keep checking the pottery at 15 minute intervals, watching for the pottery to turn darker and firm up. It may take an hour or longer.
If you are using uncoloured clay, try beating an egg and brushing that on the outside of the piece. This turns the piece a light brown colour when baked.
Always use oven gloves when removing the baking tray or touching the pot in the oven. The high temperature of the oven and the clay piece may cause burns.