Prepare a baseball-size amount of air-dry clay. Using a clay tool or a butter knife, slice the ball of clay in half. Be sure to cover any clay that you are not currently working with to avoid overdrying.
Create a ball shape with one of the halves. Stick your thumb into the center and press down to form a deep hole, but do not go all the way through the clay. Form a bird-beak shape with your hand, much like the gesture you'd make while playing shadow puppets. Use this position to pinch the rim of the clay. Slowly rotate with your other hand while pinching all around so that you gradually and evenly thin the rim. When you've formed an even bowl-shape you'll have what's known as a pinch-pot.
Create a second pinch pot with the other half of your clay. For a traditional maraca shape with a thin, hollow handle, concentrate on making the pinch pot taller and thinner. Start with a deeper hole and insert only your finger and thumb to do your pinching. Follow the same steps as you did with your first pinch pot to thin out the walls.
Form several small clay beads by rolling tiny amounts of clay onto the table. When dry, these beads will shake inside your maraca and produce the rattle sound. They should be no larger than peas. Roll each bead around until your hand removes extra moisture from them. When they are no longer sticky, place the beads inside one of your pinch-pots.
Scratch the rims of each pinch-pot with a needle tool or fork to make score marks. This will help the two pieces stick together. Wet the rims with your finger and a bit of water, then stick the two together, smoothing the sides downward until they form one smooth, hollow shape. You may need to adjust each pinch-pot slightly so that they fit together. Be sure that the beads are still inside before you seal the form.
Insert a needle tool into the bottom of your form and make several small holes. This will help the inside dry evenly and avoid cracking. Allow your clay to dry according to the package directions. It will take several days and will no longer feel cool to the touch.
Paint a base coat onto your dry maraca with acrylic paint. You will need to wait for one side to dry before you turn it over and paint the other side. When the entire form is covered, apply a second coat to any transparent areas and let dry.
Paint decorative designs onto your maraca. These can be simple dots or more complicated images, depending on your taste and ability. Even simple patterns will look good when applied neatly with bright color.
Apply a coat of acrylic gel medium over your decorated maraca. Once again, you will have to wait for one side to dry before you can paint the other. Do not worry if the topcoat appears milky. It should dry to a clear, shiny finish. The finish will protect your design and give your instrument a more polished appearance.
Shake your finished maraca and listen to the unique sound that the hidden clay beads make. Add ribbons or bells to the handle, if desired.