It is a sphere most often made of glass but it can be of any material as long as it is translucent. The best results often appear with balls made of natural crystal (but which are more expensive). It is important that the sphere is homogeneous, i.e. that it does not contain air bubbles. Its shape may be slightly elliptical, which can help prevent light reflections. A ball of a certain size may be more pleasant to use, but small ones (up to a radius of 1 centimeter) also work. Although the ball may be of different colors, the translucent ones are more suitable.