Types of Pearls

Pearl culturing has brought a wide variety of pearls to the marketplace at an affordable cost. The variety of pearls depends on the type of shellfish that they are created by, the environment as well as the area they come from. The main differences are in luster, color, shape and size.

The most common types of pearls available on the market today are Akoya pearls, South Sea Cultured Pearls, Black South Sea Cultured Pearls, Freshwater Cultured Pearls and Conch Pearls.

Akoya Pearls are produced by the Japanese Akoya oyster and range from 2 to 10 mm in size. They can be white, cream, green, silver, pink or gold. These pearls are appreciated for their luster as well as the depth of their color.

South Sea Cultured Pearls are some of the largest pearls available and can easily reach diameters over 10 mm. The reason for this is because they are grown in large oysters known as Pinctada Maxima. They live in warmer waters, especially in the South Seas. They can also be found off the coast of Australia, the Philippines and Indonesia. Most pearls from this area are produced by silver lipped pearl oysters. However, gold pearls are grown in golden-lipped pearl oysters. The latter are extremely valuable due to their rare gold color.

Black South Sea Cultured Pearls are similar to regular South Sea Pearls except that they are grown in black-lipped Pinctada Maxima oysters. They range from 8 – 15 mm in diameter and are quite rare because they are difficult to farm. These pearls can be blue, green, violet or combinations of these colors with the most sought after being iridescent green.

Freshwater cultured pearls originate, mostly, from China and are grown in Hyriopsis Cumingi mollusks. They are usually oval shaped and between ten and fourteen pearls can be grown at a time.

Conch pearls are quite unique and originate in the Caribbean or the Gulf of Mexico. They are produced by the Queen Conch and have a structure that is flame-like in appearance so that it appears as if there is a flame burning on the surface of the pearl.

Akoya Pearls

The Akoya pearl is grown in Pinctada fucata martensii oysters, which are the smallest pearl-producing oysters known to man. They are highly valued for jewelry because they are usually perfectly round, making them ideal for necklaces, bracelets and earrings. However, this doesn’t mean that these lovely pearls aren’t available in other shapes such as semi-baroque, semi-spherical and baroque.

Akoya pearls are mainly considered to be a Japanese pearl, even though China also has a high production of these pearls. The oyster itself lives in waters that have quite a low temperature which tends to fluctuate according to the season.

These pearls have a unique structure which gives them a completely different luster and color compared to other pearls. The latter is caused by the crystals of aragonite that form in the water due to seasonal change. The ideal Akoya pearls are considered to be some of the most beautiful pearls available.

Akoya pearls range in size from 2 mm to 9.5 mm, which makes them quite popular for use in jewelry. However, the most commonly used Akoya pearls for jewelry are those between 5 and 8 mm in diameter.

These pearls are also available in a wide range of colors as well, from blue to pink, rose, white, silver, gold and many more. The color palette is owed to the nacre structure and this is why producers spend a lot of time trying to get the right proportions of the conchiolin and the calcium carbonite within the nacre to create these different colors.

Likewise, the value of the Akoya pearl increases with the thickness of the nacre, thus the thicker the layers the higher the value of the pearl will be.

Akoya pearls are cultivated via nucleation with a tiny speck of shell from another oyster, which is polished into a round bead. Each oyster is implanted with approximately 3 beads, depending on the size of the shellfish itself. The incubation period is between 6 – 18 months, after which the pearl can usually be harvested. The longer the oyster is left, the higher the chances of a pearl forming and the greater its beauty will be. However, the longer time span also involves higher risks including damage to the oyster from various environmental conditions. The best Akoya pearls have been allowed approximately two years to grow.

Cultured Pearls

The majority of pearls available on the market today are cultured pearls. The latter are the result of a procedure developed in the early 1900s by a British biologist and then put into application and popularized by Kokichi Mikimoto.

To begin the pearl growing process, farmers must implant an irritant in the mollusk, such as a mother-of-pearl bead, a piece of shell or tissue. The irritant activates the mollusks defense mechanism which then creates a pearl sack to isolate the offending material and begins to deposit nacre on it, to stop the irritation.

Both freshwater and saltwater cultured pearls are available, each grown in different types of mollusks. Freshwater cultured pearls are grown in mussels and, of course, in fresh water. Due to the fact that mussels are much smaller than marine shellfish used for the same purpose, freshwater cultured pearls tend to be quite smaller than their saltwater counterparts. However, a single mussel can produce more than twenty pearls in a single year.

Saltwater cultured pearls are usually grown in oysters and only one pearl can be created at a time. This makes saltwater pearls quite rare and thus, they tend to be quite a bit more expensive. The main producers of saltwater cultured pearls are Tahiti, Thailand, Australia, Burma, the Philippines and Indonesia.

The advantage of cultured pearls is that ideal conditions can be provided for the shellfish which results in a much shorter development time and, quite often, specimens that are much nicer than their wild counterparts. Even though the development time is much shorter it can still take a few years for the pearl to grow and they should definitely not be harvested in advance because this will compromise the quality and beauty of the pearl.

South Sea pearls can take anywhere from two to three years to form, while Chinese freshwater pearls require between 18 and 24 months to develop. However, pearl farmers feel that the longer a pearl is allowed to develop, the higher the quality of the pearl will be.

Freshwater Pearls

Freshwater pearls tend to be smaller than their saltwater counterparts and usually have a more irregular shape. They can be grown in a variety of mussels and are the result of twenty or more tissue implants in a mussel. The results are varied from small, rice sized pearls that have a crinkly surface to slightly larger, smooth pearls. It takes anywhere from 2 to 6 years for the pearls to mature to full size and each mussel can produce up to 50 pearls.

Freshwater pearls have been around for thousands of years, with the earliest record of freshwater pearl harvesting dating back to 2206 B.C. in China. The Chinese have also improved the technique of freshwater pearl culturing to create much higher quality pearls which are now quite comparable to their more expensive saltwater counterparts.

The advantage is that freshwater pearls are usually much cheaper when compared to saltwater pearls but still hold the same beauty. Another advantage freshwater pearls have is that they are very durable and have a high resistance to chipping, deterioration and wear.

Freshwater pearls, though, require longer cultivation periods to create larger pearls. For example, for a pearl under 3 mm, up to two years are required, 3 – 5 mm needs 2 – 3 years, 5 – 7 mm requires 3-4 years, 7 – 9 mm requires 5 – 8 years, while the very rare pearls over 9 mm need between 8 and 10 years. They are also available in a wide range of colors. For example, Chinese freshwater pearls can be orange, lavender, pink or white. Round freshwater pearls are quite rare with approximately 3% of a total yield of 600 tons of pearls being considered round. Of these, less than 5% are considered to be high quality.

Natural Pearls

Natural pearls are quite unique among gemstones as they are “grown” inside a living being rather than being a mineral byproduct. Pearls that are produced naturally are, essentially, a by-product of the defense mechanism of different shellfish against a, usually, organic irritant is lodged within its fleshy tissue. These irritants can be either a piece of shell, bone, scale, corral or even a parasite. Likewise, damage to the shell of the mollusk can also lead to the production of a pearl.

The mollusk surrounds the “intruder” with a pearl sack and then secretes nacre which surrounds the foreign particle and then hardens. The mollusk continues to secrete this substance which surrounds the particle in multiple layers until it is no longer an irritant to the shellfish. Thus, the final result is a beautiful and highly valuable pearl.

In the wild it can take much longer for a pearl to be formed than under the controlled conditions of a farm. Additionally, over-harvesting of pearls has led to almost a complete depletion of natural pearls. They are so rare now that no more than one in maybe ten thousand oysters will produce a pearl while only a tiny percentage of these pearls are jewelry grade.

The main difference between cultured and natural pearls is that the latter tends to have a much thicker layer of nacre. This is due to the fact that often the irritant that is introduced artificially into an oyster is often quite a bit larger than a natural irritant as pearl farmers attempt to shorten the time it takes to grow a pearl. Even with the controlled environment it still takes a few years to grow a jewelry grade pearl.

Natural pearls are extremely rare and thus highly expensive. In fact, most natural pearls available today are vintage pearls as the majority of jewelry makers rely on cultured pearls. It is highly risky to purchase natural pearls and so expensive that it is often not worth it.

South Sea Pearls

South Sea Pearls are grown in large saltwater mollusks such as the silver or gold-lipped pearl oysters and the slightly smaller black-lipped pearl oysters. They yield large pearls with a diameter of over 10 mm and the common colors these pearls display include white, silver, cream and yellow from the silver and gold lipped pearl oysters. Black-lipped oysters produce pearls that vary in color from silver, brown, gold, grey and black.

The largest producers of South Sea pearls are Australia, Indonesia, Philippines and Myanmar. French Polynesia is the largest producer of black South Sea pearls.

White South Sea Pearls

From a value viewpoint, Australia is the world’s largest producer of white South Sea pearls, even though Indonesia leads in terms of actual weight production. However, Australian pearls have a much higher value due to quality.

The Australian white South Sea pearl has an average diameter of 12 – 14 mm but there are quite a few pearls that are over 20 mm in size. This pearl has a nacre thickness of approximately 4 mm which results in a unique luster and orient. The thicker the layer of nacre, the higher the quality of the pearl, which is why Australia’s production is considered so valuable.

Australia also produces a range of white South Sea half-pearls which are available in a variety of interesting shapes that can grow up to 25 mm in diameter. Additionally, there are quite a few highly interesting by-product pearls of the culturing process, known as Keshi, that come in interesting baroque shapes and are considered to be designer ready.

Black South Sea Pearls

Black South Sea pearls are grown in black-lipped pearl oysters which are found in tropical Indo-Pacific waters from the Persian Gulf to the Gulf of California and from Japan to southern Pacific islands. The main producer of black South Sea pearls is French Polynesia, where pearl farming began in 1961.

Black South Sea pearls are extremely difficult to culture with an average of 40 pearls being harvested for every 100 oysters that are seeded. Of the 40 pearls obtained approximately 8% will not be commercial grade, 15% will be round, 50% will be semi-baroque with the remainder being baroque. They range in color from pale grey to silver, iridescent brown, purple and black. The pearls range in size from 8 to 16 mm but the majority have a diameter of 9 - 12 mm.

Golden South Sea Pearls

The main producers of golden South Sea pearls are Indonesia and the Philippines. The higher quality golden South Sea pearls have a diameter from 9 to 14 mm and are golden in color with a dark orange or reddish tint.

They are quite rare because the production of these pearls has significantly decreased because farms are using white-lipped oysters which are laboratory bred to increase their production of white pearls which are easier to sell. The result is that only up to 40% of these oysters can produce cream to golden colored pearls and only 10% of these are pearls that feature a nice golden color.

Due to the decrease of availability of these golden South Sea pearls, many farms are now treating off-colored South Sea pearls to create golden pearls. They are either bleached or dyed to create the desired color. The actual color of the pearl can be determined by examining the drill hole.

There are a few key factors one should look out for to determine whether or not the pearl has been color treated. First, naturally golden pearls have an even color distribution while those that have been treated often have slightly darker spots of color. Second, natural golden pearls have an even fluorescence when under LWUV, while treated pearls will display an uneven fluorescence. Additionally, an expert can examine the reflectance spectrum of the pearl to determine the absorption maxima of the pearl. Natural pearls have a high absorption rate while treated pearls have a weak or non-existent absorption rate.

Imitation Pearls

The most common imitation pearls are made from glass, plastic or shell spheres that are coated with an imitation of nacre known as essence d’orient. The latter is made from the fine film of guanine crystals that coat the scales of the bleak, a small fish that is found in the Seine.

Other effective pearl imitations are made from thick mollusk shells of different colors. The shell is ground and polished into different shapes and they are sold as coconut pearls.