The Prayer bowls are made of a metal amalgam consisting of a Bronze (copper and tin)alloy, which may consist of Silver, Gold, Nickel Mercury, Iron, (sometimes Meteorite Iron) Powdered gems and prayer. This Mixture is heated into a disk then and hammered into shape.
They are also called standing bells because they are right side up.
They are multiphonic instruments , put simply they produce several notes at once. Which can have a psychoacoustical effect on the brain, thus entraining one to a sense of peace and harmony.