Dumbek was originally made of baked clay, and on top of it from calf, goat or fish skin. Recently, metal dumbecks made of aluminum or copper have become popular, and a special plastic serves as a membrane. Metal dumbecks with a plastic membrane are very advantageous in that they can be adjusted by controlling the degree of membrane tension using bolts. Sometimes something like a tambourine is placed inside the dumb-back - small removable metal plates that tinkle pleasantly when played.