The qualities that determine the overall value of a natural or cultured pearl or a piece of pearl jewellery are size, shape, colour, lustre, surface quality, nacre quality and for jewellery with two or more pearls matching. Pearls can be produced by layers of nacre in oysters, clams, or muscles, in freshwater or saltwater environments. This process can occur naturally, or be encouraged by placing a bead into a mollusc shell. Cultured pearls have been produced since the 1890s, patented by Kokichi Mikimoto.
Natural and cultured pearls can have white, golden, grey, brown and black body colours. These body colours can be altered through the varying iridescent tints of the pearl that can include pink, green, blue and lilac. Pearls are one of the most popular gemstones, and have long been associated with purity, beauty and love. The pearl is one of the birthstones for June and they are gifted for thirty-year wedding anniversaries.