October 22, 2020

Cultured pearl and natural pearls


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Not only are Tahitian cultured pearls not exclusively black, they’re also not grown in Tahiti. Called ‘black’ because of their exotic dark colours, that can range from iridescent emerald green, sea green, pale silver blue, melon, peach-copper, pink, cranberry, bordeaux, indigo and aubergine, to dark green and deep midnight black. And they’re grown in the lagoons of small islands that are part of a group known as French Polynesia. Tahiti, the largest island, serves as the group’s centre of commerce, and not as a pearl growing hub.

Tahitian pearls are cultivated for two to five years in Pinctada margaritifera cumingi, a giant black-lipped oyster native to French Polynesia.

Today, the most sought-after Tahitian cultured pearls are dark green-grey to blue gray with rose or purple overtones. Pearl colours are determined by several factors, including variations in the host oyster, colour variation of the implanted donor mussel tissue, the number and thickness of nacre layers, and variations in growing environment such as temperature and water quality.

At an average size of 8mm-14mm, Tahitian cultured pearls, especially those specimens that are gem-quality and round, are very expensive. According to the latest information from the Gemological Institute of America, up to 40 percent of implanted black-lipped oysters produce a gem-quality cultured pearl, but only about 5 percent of the pearls they produce are round. And only 1-2 percent of the entire crop will result in round cultured pearls of the finest quality.

Natural pearls are formed when an irritant, such as a parasite, makes its way into a pearl-producing animal such as an oyster or mollusk. To protect itself, the animal coats the irritant in nacreóa combination of organic substances that also makes up what we call mother-of pearl. Over time, the layers of nacre build up around the intruder and eventually form the organic gem we all know as the pearl.

Cultured pearls are formed in the same way as natural pearls, but they get their start not by chance, but deliberately, when man intervenes with nature. To produce cultured pearls, a skilled technician, called a nucleator, induces the pearl-growing process by surgically placing an irritantóa mother-of-pearl bead and a piece of mantle tissue, usually into a mollusk. The animal is then placed back into the water and monitored, cleaned, etc. until the pearl is ready to be harvested.

Natural pearls can be very beautiful, but due to over fishing, pollution and other factors, they are a rare find indeed. Nearly all pearls sold today are cultured pearls. There are two main types: freshwater and saltwater. South Sea cultured pearls, Tahitian cultured pearls and akoya cultured pearls are all types of saltwater pearls.

Freshwater cultured pearls rival the beauty of their saltwater cousins. Due to improvements in culturing techniques, freshwater pearl farmers are producing beautiful, round, lustrous pearls that are a vast improvement over the wrinkled, rice-krispie-shaped gems that typified the freshwater pearl crop of the not-so-distant past.

Produced mainly in China, freshwater pearls are often nucleated, or implanted, with mantle tissue only (rather than a mother-of-pearl bead). Because they do not contain a starter bead, tissue-nucleated freshwater pearls are 100% nacre. This gives them a beautiful luster and a durable surface that won’t easily flake or peel to reveal the inner bead. By contrast, pearls that are bead-nucleated and harvested too soon often have only a thin coating of nacre that will flake or peel. This is a major problem: Unlike many other gemstones, pearls cannot be polished back to perfection.

Freshwater cultured pearls come in many beautiful natural pastel colors including cream, white, yellow, orange, pink and lavender. White pearls are bleached to enhance their natural shine. Black freshwater cultured pearls are treated with dye or heat to produce their inky color.

Overall, freshwater pearls are more plentiful than other pearl types, thus they are generally more affordable.

South Sea pearls really are golden

Pearls produced in the aptly named ‘gold-lipped’ oyster (P. maxima) can be a gorgeous creamy yellow, referred to as ‘golden’ in the trade. (The silver-lipped variety of P. maxima produces beautiful silver or white pearls.) Grown in the South Seas that stretch from the southern coast of Southeast Asia to the northern coast of Australia, these pearls are grown in one of the biggest oysters used in pearl culturing. Because they can accept a larger bead and secrete nacre faster than their smaller counterparts, these big oysters produce large pearls of exceptional luster and beauty. South Sea pearls’ thick coating of nacre gives the gems a wonderful luster, or glow, that appears to come from deep within the pearl. The warm waters, abundant food supply and low pollution levels of the South Seas also help these oysters produce beautiful cultured pearls.

Although Australia produces 60% of the world’s South Sea cultured pearls, Indonesian farmers work more with the gold-lipped oyster, and thus produce more golden pearls. The silver-lipped variety produces equally beautiful pearls that come in white to silver and often have rose, blue or green overtones. Aside from giving them a light wash, pearl farmers do not treat South Sea pearls after harvest.

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