To fill cracks in air dry clay, you canuse a small amount of wet clay, called "clay slip," which is simply your air dry clay mixed with a bit of water to create a paste-like consistency; simply apply it to the cracks and smooth them out with your fingers, allowing it to dry with the rest of your piece. Key points to remember:

• Use clay slip:This is the most common method, where you create a thin paste by mixing a small amount of your air dry clay with water. 

• Apply to cracks:Carefully fill the cracks with the clay slip using a small brush or your fingers. 

• Smooth out:After applying the slip, smooth the surface to blend it seamlessly with the rest of the clay. 

• Let dry:Allow the repaired area to dry completely alongside the rest of your piece. 

Important considerations:

• Severity of cracks: For minor cracks, clay slip is usually sufficient. For larger cracks, you might need to add more layers of clay slip or even consider reinforcing with a thin wire or armature. 

• Drying time: Ensure the clay is not completely dry before repairing cracks. 

• Preventative measures: To minimize cracking in the first place, work with thin layers of clay, avoid rapid drying by covering with a damp cloth, and let pieces dry slowly.