Pearl Guide

How a pearl is created

Pearls, whether natural or cultured, are made inside a mollusk.  Mollusks can be oyster or mussels and must be the type that builds a mother-of-pearl lining on the inside of the shell.  If they can build mother-of-pearl, they have the ability to create nacre, the semi-hard outside layers of a pearl.  Natural pearls form when a parasite or another foreign matter irritates the mollusk to secrete layers of nacre to smooth over the irritant.  The majority of pearls on the market are cultured pearls.  Two types of cultured pearls exist, saltwater and freshwater.  Cultured saltwater pearls have humans that insert a bead nucleus and a piece of mantle tissue into the mollusk.  “The mantle is an organ within a pearl-producing mollusk that manufactures both conchiolin and calcium carbonate-the essential building blocks of both the mollusk’s shell and pearls (GIA, 2000; Pearl Grading: Pearl description system manual, p. 2).”  Freshwater cultured pearls have only a piece of mantle tissue inserted into the mussel that irritates the mollusk to produce the layering nacre.     

Cultured Pearl Products

Akoya-Usually cultivated in China and Japan, the typical size ranges from 6 mm – 7 mm, but other sizes do exist.  The body color is usually white to cream but other natural colors exist, including gray, blue, and yellow.

South Sea-Ranging in color from white to golden, yet other colors can be attained, and sizes include 8 mm to 15 mm.  The principal commercial farming areas are in the Philippines, Australia, and Indonesia. 

Tahitian-Cultivated primarily around the islands of French Polynesia, these pearls range in color from white to black to other colors including green and purple.  The spectrum of sizes is 8 mm to 14 mm, although larger sizes do exist in limited quantities. 

Freshwater-This type of pearl has the most variety of sizes, shapes, and colors.  While Japan and the United States produce small quantities, most freshwater pearls are sourced from China. 

Keshi-Irregularly shaped pearls that come in a wide range of size and colors.  Keshi means “poppyseed” in Japanese.

Blister-Blister pearls grow attached to the mollusk’s shell.  One side is flat and nacre-free and can be from freshwater or saltwater mollusks.

Mabe-These pearls are cultured blister pearls that have been cut from the shell and the nucleus has been removed.  The resulting void then has a backing of mother-of-pearl epoxied to the area.  

Seven Value Factors

These seven factors help jewelers determine a fair price for the product.  **Please note the images found at the end of this article, for quality visualization. 

  1. Size-Measured in millimeters (mm); Measure diameter for round pearls and length and width for other shapes.  For multiple pearls in a product, a range is given (7 – 7.5 mm).
  2. Shape-Seven standard shapes fit into three categories:


Round-appears round to the eye.  For a strand, roll the pearls on a pad under your fingers and watch the outline for pearls that break the plane. 

Near-round-appears almost round to the eye.


Oval-symmetrical, rounded, oblong shape.

Button-symmetrical, flattened, or slightly flattened, circular shape.  Can be a high button or a low button.

Drop-symmetrical, rounded, pear-shape.  Can be a long drop or a short drop.


Semi-baroque-non-symmetrical, off-round, slightly irregular oval, button, or drop shape.

Baroque-non-symmetrical shape-will have a noticeably irregular appearance. 

For any other shape that does not fit into these shape categories, describe the shape as it appears: coin, bar, cross, for example. 

  1. Color-three components of color exist, bodycolor, overtone, and orient. Bodycolor is the overall color of the pearl.  Overtone is the noticeable translucent color found over the bodycolor.  Orient is the iridescence found on or just below the surface.  Not all pearls display all three characteristics. 
  1. Luster-four categories represent luster, the intensity of light reflected from the pearl’s surface.  Note the crispness of light above the pearl reflected on the pearl surface. 

Excellent-reflections are bright, sharp, and distinct.

Good-reflections are bright but not sharp.  They are slightly hazy around the edges.

Fair-reflections are weak, hazy, and blurred.

Poor-reflections are dim and diffused. 

  1. Surface quality (blemishes)-“Most pearls have surface characteristics, or irregularies.  Surface condition is judged by the size, number, location, visibility, and type of blemishes.  Blemishes affect the pearl’s appearance while some affect both appearance and durability.  Few pearls are completely blemish-free (GIA, 2000; Pearl Grading: Pearl description system manual, p.6).”  When viewing, consider the size, number, location, visibility, and types of blemishes.  Four ratings exist for surface quality:

Clean-blemish-free or minute surface characteristics difficult to the trained eye. 

Lightly blemished-minor surface irregularities to the trained eye. 

Moderately blemished-noticeable surface characteristics; a few might be quite noticeable.  

Heavily blemished-obvious surface irregularities; durability might be affected.  

  1. Nacre quality-determined by its thickness and layering.  If the nucleus is visible, the nacre is too thin.  A chalky appearance might indicate thin nacre or poor nacre layering.  Three quality classifications exist:

Acceptable-nucleus not noticeable; no chalky appearance.

Nucleus visible-the bead nucleus is evident through the nacre; pearls show blinking when rotated.

Chalky appearance-pearls have an obvious dull appearance. 

  1. Matching-describes the uniformity of pearls in jewelry.  The six other value factors need to be consistent throughout the jewelry piece.  Matching does not impact single pearls. 


Bleaching-an extremely common treatment to white pearls; bleaching is a way to clean and brighten the pearl surface and it lends a more uniform look to matched pearls.

Dyeing-alters the basic pearl color.

Irradiation-permanently alters the pearl’s color. 

Coating-enhances the luster of pearls and are usually used on lower quality goods.  The effect might not be permanent. 


Care and Cleaning

Consult the How To Clean Pearls video at


GIA, 2000; Pearl Grading: Pearl description system manual. 

GIA, 1999; Pearls: Value Factors