The idea of culturing pearls was not a new one. It is said that Arabs in the Persian Gulf seeded oysters with tiny pearls in the 3rd Century and that the Chinese were putting little Buddha icons inside mussels to get pearl covered shapes in the 12th century The Swedish naturalist, Linnaeus, in 1761 experimented with placing foreign objects into oysters.
The problem, however was that the oysters or mussel in which the object was planted died when opened again and could not be re-used. It was the Japanese at the end of the 19th century who began to explore techniques to open an oyster, seed it and let it close, harvest it and then start the process again.
Kokichi Mikimoto was an entrepreneur who wanted to produce cultured pearls. He produced his first half pearls in 1893 and opened a shop in Tokyo in 1899 selling them to foreign tourists. Around the same time, an amateur enthusiast, Tatsuhei Mise, and a scientist, Tokichi Nishikawa, began separately to work on processes to develop spherical cultured pearls. In 1907, both applied for a patent but a dispute arose due to similarities in the two processes. They agreed to combine their application but Mise died in 1909. In 1916, Mikimoto applied for a patent for spherical pearl culturing and was awarded one 50 days before the Mise-Nishikawa application was granted. Nishikawa by this time was Mimimoto’s son-in-law. There is some dispute about when cultured spherical pearls were first commercially produced but it was certainly not before 1921 and was more likely 1925.
So, spherical pearls (and most half pearls) and seed pearls in antique jewellery, that is, 100 year old jewellery, will be natural pearls, either saltwater or freshwater. In 1916, Mikimoto’s patent for spherical cultured pearls meant that cultured pearls began to appear on jewellery from then on in a few cases but it was not the mid 1920s that the commercial use began. The Art Deco period, covering 1920 to 1935, saw the first significant use of cultured pearls in jewellery.
When purchasing antique jewellery, then, most of the pearls should be natural pearls. You need to be aware, though, of imitation or fake pearls. Fake pearls, created from glass or polished shells, then coated with a varnish made from ground fish scales, were common in Elizabethan times, particularly for sewing onto clothing but also for jewellery. Glass pearls continued to be used into the beginning of the 20th century when cheap cultured pearls and plastic pearls started to be used instead.
Natural pearls are still sold but mainly in antique jewellery. Always expensive, the price for natural pearls has soared and a thin antique necklace of natural pearls can cost 1000s of dollars at an antique shop or auction.
Good references for pearls are:
- Pearls by Beatriz Chadour-Sampson
- Gems: Their Sources, Identification and Description by Robert Webster
- Gems and Ornamental Materials of Organic Origin by Maggie Campbell Pedersen
- The Underworld of Gems: Part II, Thomas Naylor,  53 Crime Law Soc Change 211-227.