The majority of pearls used today are farmed and not naturally grown. Sadly natural pearls are becoming less common due to years of over-fishing and the great demand for perfectly round pearls. During the start of the 20th century, a new process for growing pearls was developed resulting in what is now known as cultured pearls. Essentially the process involves inserting an irritant into an oyster and then caring for that oyster until it has developed a pearl. Today, almost all pearl jewellery uses cultured pearls.