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Pearls: Buying Guide

June 03, 2019

Pearls: Buying Guide

Here you will discover the differences between a cultured pearl vs natural pearl, how pearls are formed, types of pearl, their main characteristics, quality of pearls (nacre pearl, pearl luster, natural pearl colors, pearl size) ,  varieties of cultured pearls (cultured freshwater pearl and cultured saltwater pearl),  history, etymology, etc.

Pearls are a Mother Nature‘s Miracle, rare treasures that come from the seabed and that have been adorning our bodies for millennia. 

Pearls are the birthstones that correspond to the month of June.


  1. History of the Pearl
  2. Etymology
  3. Origin and Formation of the Pearl
  4. Ecosystem of the Organisms
  5. History of the Cultured Pearls
  6. Cultivation Process for the Cultured Pearls
  7. Cultured Pearls
    1. Akoya Cultured Pearls
    2. Tahitian Cultured Pearls
    3. South Sea Cultured Pearls
    4. Pearls of the Sea Of Cortez
    5. Cultured Freshwater Pearls
    6. Keshi Pearls
    7. Mabe Pearls
  8. Main Production Areas for Natural Pearls
  9. Pearl Classifications Quality of Pearls
  10. Pearl Treatments
  11. Imitation Pearls
  12. Famous Pearls
  13. Care and Maintenance of Pearls
  14. Pearl Birthstone
  15. Pearl Nomenclature CIBJO
  16. Physical Properties of Pearls
  17. Structure of Natural Pearls and Culture Pearls
  18. Pearl Units of Weight


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We can find writings that refer to pearls from as far back as 2500 B.C., so they have been adorning our bodies for more than 4 millennia.

In India, the pearl was associated with religious beliefs and both men and women wore them.

Tahitian Pearl


Alexander Magnus took pearls to ancient Greece, where they were in fashion until the fall of the Roman Empire, after which they were no longer used. In the Renaissance (15th-17th centuries) an interest in pearls reappeared.

At the end of the 19th century - early 20th century, there was a great demand for pearls, leading to the overexploitation of natural pearl banks. This involved the fall of the "proliferation" of natural pearls and coincided with the appearance of the cultured pearl on the markets (1910-1920).



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The name comes from the Greek word margaron, which means daughter of the sea, in reference to its origin.

The Latin translation of margaron is margarita (marguerite in English)

The pearl was in fashion in both ancient Greece and during Roman times. Roman women often wore elongated pearl earrings (pear-shaped). From here, the name was changed from margarita to perula (from pear), referring to the pearl's form. Over time, the name came to be pearl.

White South Sea Pearls 10 mm



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A pearl is an organic animal origin gem. Pearls are originated through a biological process that occurs as a result of a mollusc’s (lamellibranch or bivalve molluscs) defensive reaction, which isolates any foreign body that is inserted into its tissues (grain of sand, pieces of shells, larvae, etc.).

To defend itself, the body surrounds the foreign object with epithelial tissue and creates a depression in its mantle. This depression will continue to deepen until the foreign body is trapped in the mantle of the body and surrounded by epithelial tissue. The cells of the epithelial tissue secrete nacre, which is deposited around the foreign body in layers, giving a concentric structure to the pearl that is being formed.


These layers are formed by small tabular aragonite crystals (CaCO3) in a network of conchiolin (a set of complex proteins secreted by the epithelial tissue).

group of cultured pearls

The normal growth of a pearl is between 4 or 5 layers per day (each layer is about 0.5 µm thick). The timeframe needed to produce a pearl is about 6 months (the rest of the time they hibernate), so that in three years the pearl grows 1.08 mm. The growth time for a pearl measuring 10 mm would be about 30 years.

The growth time for South Seas Pearls is almost twice as fast.



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Both natural and cultured pearls have the same ecosystem:

Warm and clean waters between 20ºC and 25ºC with depths of between 10 and 20 meters. The extreme temperatures to ensure these organisms remain alive are:

   10ºc minimum temperature and  28ºc maximum temperature

When temperatures are between 10 and 18 °c, oysters hibernate and their active period lasts for 6 months of the year (production period of pearls).

An oyster’s lifespan can range from 7 to 10 years, but can even extend to 30 to 40 years, depending on the species.  Due to climate change and pollution, their cultivation is really complex.



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Modern cultured pearls are the result of the discoveries made by the Japanese researchers Tatsuhei Mise, Tokichi Nishikawa and Kokichi Mikimoto.

The Japanese researcher Kokichi Mikimoto was the first person to successfully commercialize cultured pearls. He devoted 20 years to researching the cultivation of spherical pearls. Between 1910 and 1920 he began the cultured pearl trade.

Mikimoto Kokichi


The production of cultured pearls started with Pinctada martensi oysters (Akoya oysters). This oyster is about 7cm in diameter and has a life cycle of between 7 and 8 years.



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Cultured pearls are produced on farms where oysters are also cultivated. In most cases, these oysters are grown from the time they are young, although in some areas (such as Australia) the oysters are obtained from the natural environment.

Mollusc growth during the larval stage begins with the introduction of dry branches in the water so that the oyster larvae attaches to them. The fixed larvae begin their lifecycle and after 3 years the larva reaches adulthood.


After reaching the adult stage, the valves are opened, and a spherical core of nacre from freshwater molluscs is inserted with tweezers (the diameter will vary depending on the type of mollusc), covered in part with a little piece of epithelial tissue from another oyster and then the mollusc is left to create the coating itself.

They are housed in individual mesh pockets that are suspended from chaplets, lantern baskets, pocket nets and floating or submerged trays to protect them from predators, and immersed in water. The oysters are regularly taken out of the water to clean them and to undergo any required health treatments (deworming, antibiotics, etc.). A high percentage of oysters will die, and from the remainder, only 25-30% will produce commercial quality pearls.

The cultivation period ranges from 9 months to 8 years.




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Oysters: Pinctada fucata martensii and Pinctada fucata chemnitzii (these are the smaller oysters used in cultured pearls).
Areas: Japanese waters, China, Vietnam, South Korea and Australia.
Culture time: 9 to 16 months.
Culture layer (nacre pearl) from 0.35 to 0.7 mm.
Size: 2 mm to 11 mm (average 6 - 8 mm), Akoya Pearls over 10 mm are very rare.
Shape: Round, near-round and baroque.
Color: bodycolor: usually white and cream with pink, green and silver overtones.
Features: great lustre and perfectly round.



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Oyster: Pinctada margaritifera (black-lipped)
Area: French Polynesia and around Tahiti.
Culture time: 2 to 3 years.
Culture layer: (nacre pearl) 2 to 6 mm.
Size: 9 mm to 17 mm (average 10 mm).
Shape: Round, near-round, oval, button, drop and baroque.
Color: These pearls are unique because of its natural dark colour. While they are not black, they usually present a dominant dark green bodycolor with overtones of silver, copper and "peacock" –much like the wings of a peacock with purples and blues.

Loose Baroque Tahitian Pearl



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Oyster: Pinctada maxima (two varieties, gold and silver lips, responsible for the colour of pearl)
Area: they are grown in areas of the Indian and Pacific oceans, mainly in Australia, the Philippines, Indonesia and Myanmar.
Culture time: at least 2 years, 3 to 8 years.
Culture layer (nacre) 2 to 6 mm.
Size: 9 mm to 20 mm (average 13 mm)
Shape: Round, near-round, button, oval, drop and baroque.
Colour: White, silver and gold (Golden
), they can especially present blue, pink overtones, etc.


Golden South Sea Pearls Pair 11 mm



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Oyster: mazatlanica Pinctada and Pteria sterna 
Area: The Gulf of California
Culture time: 2 years for oyster growth + 2 years for culture.
Culture layer (nacre) 0.8 - 2.3 mm.
Size: 8 mm to 14 mm (average 10 mm.)
Shape: Baroques (the vast majority), semi-baroque, round, near-round.
Colour: green with overtones of silver, purple, grey, copper, etc.



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The cultivation of freshwater pearls (in freshwater, non-saline medium) generally occurs in China, but also in Japan and the United States. They are obtained from the mollusc Ikekou of the genus Unio and also from the mollusc from the genus Hyriopsis, which can produce 4 or more pearls simultaneously (a freshwater mollusc can withstand 15 insertions per valve, (although the average is 5), of different colours and shapes. They require a culture time of between 2 and 6 years. They measure up to 17 mm.

Unlike saltwater pearls, freshwater pearls are usually not as round. But you can find them in all sizes, shapes and colours, at a much more affordable price than their saltwater sisters.

  White Baroque Freshwater Pearls Pair 49.21 ct 


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They form spontaneously (without a nucleus), as a result of accidental intrusion during the cultivation period. They occur in both saltwater and freshwater.

As a general rule, they are small (because there is no nucleus), their average size is between 4 to 8 mm. Those larger than 10 mm are rare and fetch premium prices. Their shape is usually baroque. They present a wide variety of colours and because everything is nacre, they have a good "“orient” and a high sheen.



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They are a hemispherical-shaped pearl, from which the nucleus has been removed. They are then filled with a resin and they will have been closed with a base of mother of pearl. They are used in jewellery for earrings and rings.

White Mabe Pearls Pear Pair 18.62



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It needs to be taken into account that very often oilfields coincide with natural areas where pearls are produced, so due to pollution oyster production rarely occurs, and the same happens with the search for them.

The main production areas for natural pearls are areas near the tropics:

The Persian Gulf, Australia, Indonesia, India, Sri Lanka, The Philippines, Malaysia, The Red Sea, Madagascar, The Gulf of California, Panama, Venezuela

Freshwater Pearls, Rio Mississippi, Scotland, Sweden, Pakistan



Until 1990, Japan was the home of cultured pearl production.

Currently, the production of cultured pearls in Japan is very low and it is China that is now the dominant producer. (China produces freshwater pearls and Japanese Akoya pearls).

However, Japan remains the largest cultured pearl distributor, even though they are not produced there. After China, the major producers of cultured pearls are Australia, Indonesia, the Philippines and Myanmar, which produce the South Sea Pearls.



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According to the pearl’s measurements (Pearl Size)
As a rule, the larger the pearl, the more expensive it is. The size depends on the variety of the oyster.

According to the pearl’s shape (Pearl Shape)
Round, near-round, hemispherical (oval, button, pear), semi-baroque and baroque. Perfectly round pearls or those that are completely symmetrical pear-shaped or drop-shaped are highly valued.

According to the pearl’s color (Pearl Color)
The pearl’s colour depends on its variety. While they have a dominant bodycolor, they often have overtones.

Depending on the pearl’s lustre (Pearl Lustre)
This is the most important factor and this factor gives each bead its unique beauty. Different varieties of pearls exhibit different lustres.

According to the thickness of the pearl's layer of culture (Nacre Pearl)
The greater the number of layers a pearl has, the greater the thickness of nacre and the better the lustre. The thickness of the layer of culture and lustre are strongly linked.

The famous "Orient" of a pearl is due to the reflection of light on its surface, plus the iridescence caused by the interference of light on the different layers of pearl and to the diffraction that occurs in the aragonite lamellae.

According to the surface finish (Surface)
Part of the texture of a pearl is the small imperfections and marks, which are evidence of their origin. These small "inclusions" depend on the pearl’s ecosystem, as small particles floating in the sea get inside the oyster. The fewer imperfections that are seen, the higher the quality and the more valuable the pearl. They are usually classified as clean, lightly spotted, moderately spotted, and heavily spotted exto-columna-izquierda
cultured pearls



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Akoya and freshwater pearls are bleached routinely, and are then cleaned and polished.
Treatments to improve the colour of the pearl:
Dyeing is to apply silver nitrate to the pearl, or other types of dyes to darken the pearl’s nacre.
Irradiation, through gamma ray irradiation on the pearl, the conchiolin is attacked and a darker colour achieved.
Treatments to improve the surface finish:
In older times, if the surface of a natural pearl was damaged, this portion of surface was extracted.
Another system to restore damaged surfaces is to heat the surface and then let it cool, and adding different coatings.


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Solid painted glass pearls.  Some date back to Roman times, today they are no longer made.

Empty glass pearls painted with several layers of an extract known as "essence of orient" (extract of a lacquer with guanine scales, from the bluefish). They are then filled with liquid wax to give weight to the piece. They are also called "Pearls of Paris", as the inventor was a French rosary manufacturer from the 17th century.

Majorica Pearls. These pearls are a glass ball that solidifies around a rotating shaft, painted with several layers f essence of orient. They can be found in different colours.

Plastic pearls, hematite pearls (imitating the black pearl), imitations of pink pearls made with the shell of the Strombus gigas.



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  • Peregrina Pearl, pearl with an unusual measurement and shape, considered one of the most valuable and legendary gems in the history of Europe. Discovered in Panama in the 16th century, it passed into the hands of King Philip II of Spain, becoming part of the crown jewels of Spain (joyas de la Corona de España). Elizabeth Taylor had it until her death. It weighs 203.84 grains (about 10g, about 51ct).
  • Imperial Hong Kong Pearl, silvery white baroque pearl, grains 510 - 127.5 ct, 26 x 39 mm and 25.5 grams. It is one of the largest quality natural pearls in the world.
  • Pearl of Asia, elongated pearl of about 240 grains (about 12 grams) discovered in the late 16th - start of 17th century.
  • Pearl of Allah, it is the world's largest known pearl. This pearl is not of gem quality. It is 24 cm in diameter and weighs 6.4 kg.
  • Pearl Abernathy or “The Little Willie Pearl”, natural freshwater pearl with a near-perfect spherical shape. 44 grains.
  • The Arco Valley Pearl, baroque pearl of 2301 grains, 575 ct. White pearl with pink and brown overtones. Presented by the Emperor of China, Kublai Khan, as a gift to Marco Polo.
  • Peart Hope, 1800 grains (450 ct). Blister shaped pearl, like a white drop, with green and golden overtones. It is currently in the British Museum of Natural History.
  • The Big Pink Pearl, The Gogibus Pearl, La huerfana (the Orphan), La pellegrina.


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Nacre is an organic matter that can "age", that is, if there is desiccation it can become dull, cracks can appear and it can lose layers. So it is very important to care for pearls, avoiding dryness and excessive moisture; pearls are sensitive to acids, perspiration, cosmetics, perfumes. They need to be kept in boxes with interiors that allow perspiration and they can be easily scratched by other pieces of jewellery. Pearls should be washed with a mild soap.

south sea pearl diamond earrings



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Pearls are associated with purity, chastity, stability in marriage, etc.

Pearls are the birthstones that correspond to the month of June. They are given as a gift to those celebrating their 3rd and 30th wedding anniversaries.

In Vedic astrology, the Pearl is related to the Moon.

Pearl and Alexandrite are the official Birthstones for JuneMore information about Birthstones


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  • Natural Pearl or Pearl
  • Cultured Pearl. These marked the beginning of the studies of pearl in the gemmological field.
  • Composite Cultured Pearl
  • Imitation Pearl



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  • Hardness: 2.5 to 4 according to the Mohs scale
  • Density: 2.66 to 2.78
  • Pearls are opaque.
  • Colors: White, pink, cream yellow, gold, blue, grey, silver, near-black, etc.
  • Lustre: From pearly to matt with some soft iridescence due to a phenomenon involving the interference of light on a thin layer.
  • Orient of the pearl: play-of-colour due to the brightness of the pearl and to the interference phenomena and light diffusion on the pearl.
  • Refractive index: 1.530 to 1.686
  • The NATURAL pearl is semi-transparent when X-rayed
  • Fluorescence: Bluish or reddish fluorescence under long wave UV light → The Black Pearl has a more reddish fluorescence.
  • X-ray fluorescence: Natural Pearls do NOT present any fluorescence, while the cultured pearl has some fluorescence at the RX because of nacre manganese acting as the nuclear.



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Micro-structure. The interior of the natural pearl is completely different from the cultured pearl, as natural pearls are concentric layers and layers of nacre, while cultured pearls are formed by a core of nacre and a few millimetres of coating.

Macro-structure. The pearl’s surface is not smooth, but presents a micro level (each layer is not fully completed), this micro level is the present in natural and cultured pearls, but not in imitation pearls.



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  • Carat, 1ct = 0.20g
  • Pearl grain, 1 pearl grain = ¼ct = 0.050g. Old weight unit. A pearl grain is the average weight of a grain of rice.
  • Momme, 1 momme = 3.75g = 18.75ct
  • Kan, 1 kan = 1000 mommes (= 3.75 kg)



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