Pearl Education

Cultured Pearls

A cultured pearl is created by inserting a round, shell bead and small bit of mantle tissue from another oyster into a mature oyster.  This process stimulates the oyster to produce layer upon layer of nacre which covers the bead, forming a beautiful and lustrous pearl.

Human intervention distinguishes a cultured pearl from a natural pearl.  Natural pearls are created when a fragment of shell or fishbone, or a grain of sand entered a pearl oyster’s shell naturally forming the core.  To protect itself from this irritant, the oyster secretes thousands of layers of nacre, the shiny iridescent substance that forms a pearl.  Natural pearls are extremely rare.

Types of Cultured Pearls

Akoya Cultured Pearls

Akoya pearls are the most popular pearl type and are favored for their brilliant luster.  Akoya pearls originated along the Japanese coast.  Their color ranges from white to cream, pink to light green, blue and silver and they are generally 3-10 millimeters in size.  Akoya pearls are distinguished by their high luster and rich color.

Freshwater Cultured Pearls

Freshwater cultured pearls differ from Akoya pearls in that they are generally smaller and less symmetrical; however, they are similar in appearance to Akoya cultured pearls in color, they are mostly round, and they look very similar to Akoya pearls when worn. Freshwater cultured pearls can be created in a wide range of colors including pinks and other pastels, various shades of brown, green and blue, as well as, the traditional white, grey, and black. Freshwater Cultured pearls are of good quality and are available for a much lower price then Akoya pearls, making them an excellent and affordable option for a self-purchase or a gift.  

South Sea: Tahitian Black

These pearls are cultured in the northern waters of Australia, Indonesia, and the Philippines. These pearls are considerably larger than Akoya Tahitian Black pearls are produced by oysters from Tahiti, French Polynesia and Okinawa and they range in size from 8-15 mm.  The oyster’s iridescent black color on the inside lip of its shell is responsible for producing the dark color of the pearl.  Tahitian pearls combine blue, green and violet tones and can range in color from light grey to gunmetal grey, silver, pistachio to peacock green, and midnight black with overtones of green, rose or blue. 

South Sea: White and Golden

Generally, South Sea pearls are either a white or golden color.  South Sea pearls are also known for their larger size, with pearl sizes of 9MM and up.  These pearls are produced in the warm waters of the South Seas by much larger oysters, which are capable of producing pearls in rare sizes and in rich colors. The color of South Sea pearls is determined by the type of oyster from which the pearl comes.  For example, large silvery pearls are produced by the Large Silver-lipped Pearl Oyster of Australia, where as golden pearls are produced by the Golden-lipped Pearl Oyster of Indonesia, Burma, and the Philippines.  

Qualities of a Pearl

There are five physical factors to consider when evaluating pearls: 

Color

Pearl colors vary and are available in a wide spectrum of colors and shades.  Some pearl shades are rarer than others and, therefore, the rarer the shade the more valuable the pearl tends to be.  The color of a pearl is determined by several factors, including the type of oyster which produced it and by a combination of light (light interference), pigments in protein, and organic material. When evaluating color, the two most important factors are richness of color and even color distribution.  Ultimately, though, it is a matter of personal preference and is the customer’s choice.

Luster

Luster is the amount of light reflected from the pearl’s surface.  It refers to both its surface glow, as well as, its inner light or deep mirror-like reflection.  Luster is perceived as the most important determinant in evaluating the quality of pearls.  If the nacre quality of a pearl is good, the pearl’s luster will generally be superior, as well, and the pearl will reflect light strongly giving off the appearance of a glow.  Pearls with low luster won’t show a reflection very well and may appear to have a milky surface.

Shape

Although many pearl shapes are available, perfectly round pearls are the rarest and, therefore, the most valuable.  Other pearl shapes include baroque, teardrop, oval and button.

Surface Perfection

A pearl’s surface is also a significant factor in determining its value.  The fewer marks and blemishes a pearl has, the more valuable it is considered.  Although marks on the surface of a pearl will lower a pearl’s grade (insert hyperlink to pearl grading system), the marks might not affect the luster or shape of the pearl and do not necessarily detract from the value of the pearl, unless the blemishes are excessive.

Size

Pearls are measured in diameter increments of millimeters (mm), but not all qualities of pearls are available in all sizes.  Although size does not affect the overall quality of cultured pearls, it does affect price.  As a general rule, the more difficult a pearl is to cultivate, the more likely it is to have a higher value.
For example, large pearls, such as South Sea pearls, which range in size from 9-15mm, have a higher value than smaller pearls.  This is because the likelihood the oyster will reject the implanted nucleus is greater and, therefore, they are more difficult to produce.

Pearl Grading System

Luster, surface perfection, shape, color, nacre quality and size are recognized in the pearl industry as the standard factors used for pearl grading.  Although a combination of those six factors is used to determine the overall quality and value of a pearl, luster and surface perfection are regarded as the most important factors.  

In 1974, however, Mikimoto (link) developed and instituted the first pearl grading system in the U.S. for Akoya cultured pearls, as illustrated by the chart below.  

Mikimoto’s grading scale defines the six factors above using four individual grade categories, with AAA representing the very highest quality while sub-grade “1” signifies a slightly more blemished version of the grade.  Based on consumer demand, Mikimoto eventually adapted the system to grade South Sea cultured pearls, as well.

Citation: http://www.mikimotoamerica.com/about-pearl-jewelry/how-to-buy-pearls/mikimoto-grading-system/