Explanatory notes
… white but may be shaded or coloured (e.g., grey, black, purple, red, yellow, green or blue). They are usually round, … by fixing a bead of mother of pearl in a sac cut from the mantle of one oyster and then inserting this sac in the … pearls whether unworked, i.e., as gathered and merely cleansed (for example, by means of salt and water), or …