Natural pearls form naturally in oysters, while cultured pearls are formed by human implantation of a nucleus. Natural pearls have thicker nacre layers and are often less iridescent than cultured pearls. Both types can look different on the inside and are in demand, but most pearls sold today are cultured. Only one in 10,000 oysters will produce a pearl, and the appearance of both types depends on the water and food conditions where the oyster lives.
Natural and cultured pearls grow inside oysters. However, natural pearls are naturally formed in oysters, while cultured pearls are formed in oysters by human implantation of a nucleus. The other main difference between the two is that a natural pearl has thicker nacre or nacre layers than a cultured pearl.
The nacre layers formed in all pearls are made up of microscopic crystals. The iridescent finish on the pearls comes from the perfect alignment of the crystals so that they reflect light. Mother-of-pearl is 90% calcium carbonate and 10% water and other organic substances. The outer layer of can look very different between natural and cultured pearls; Natural pearls are often less iridescent than cultured ones.
Natural and cultured pearls can also look extremely different on the inside. Sometimes strong light is enough to see inside a pearl, but usually a pearl’s inner layers can only be seen with special equipment similar to X-rays. Cultured pearls often show a narrow brown line around the nucleus, while natural pearls do not have any of these growth rings.
The Japanese invented the core method process in pearl harvesting. The nucleus that humans implant in the oyster is generally larger than a natural pearl, as the nacre layers will not be as thick in a cultured pearl. Otherwise, the oyster covers both mother-of-pearl as a means of warding off the foreign irritant.
Contrary to popular thought, a grain of sand is usually not irritating enough to an oyster to form a pearl. Natural pearls are often formed from a fish scale, parasite, or piece of shell. Both natural and cultured pearls are in demand in today’s market, but most pearls sold today are cultured. Unless the pearls are over 80 years old, it’s a good chance they are cultured rather than natural.
Natural pearls are rare, and most shellfish capable of producing pearls are nearly extinct due to pearl hunting in the 19th century. Bahrain is one of the few remaining countries that has divers searching for natural pearls. Any type of pearl can be expensive since not all oysters make them. Only one in 10,000 oysters will produce a pearl, and only a few will have the desired luster and shape.
The appearance of both natural and cultured pearls depends not only on the irritant, but also on the water and food conditions where the oyster lives. Some Chinese pearl farmers grow freshwater cultured pearls that are very thick in nacre because they move the pearl core as it grows in the oyster so that the resulting shape is more evenly rounded. Akoya pearls are cultured pearls produced by small Japanese oysters. Rounded pearls are implanted in oysters so Akoya pearls are generally rounder than most cultured freshwater pearls.
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