Pearl Grading: Shape
Pearl Grading System
Pearl grading is very similar to the "4 C's" of diamond grading in that the pearl grading system takes into consideration several key categories of qualitative comparison analysis. The pearl grading system consists of five main categories:
2. Pearl Shape
Shape is one of the principle determining factors in a pearl's value after luster. With all other factors being equal, the general rule is that the rounder the pearl, the more valuable it is. Pearls come in a wide variety of shapes, each having a specific designation.
A "round pearl" (A) is perfectly symmetrical and should roll in a straight line along a slightly angled surface. Only a small percentage of total pearl production will yield perfectly round pearls. This is because the eventual shape of the pearl is determined by a number of highly variable factors which occur inside the oyster, as the pearl is developing.
As the pearl develops it will tend to assume the same shape as its "nucleus" which is typically round. The nucleus is the irritant which was placed inside the oyster to initiate the formation of the pearl. If the nucleus is not perfectly round, the resulting pearl is likely to reflect, and amplify its irregularity. Additionally, the pearl's positioning within the oyster's body also plays a role in determining its shape. If the pearl develops against the shell wall it will tend to become flattened on that side.
There are various terms to describe pearls that are "visually" round to the untrained eye, yet are slightly out-of-round. These terms are:
- Almost Round (B)
- Off-Round (C)
- Roundish (C)
All of these terms are used to indicate pearls that are "roundish" to varying degrees, and considered to be "round" as a basic classification.
Other grading terms are used to describe pearls that are slightly to significantly out-of-round or which indicate an extended round shape but still look somewhat round. These terms are:
- Egg Round (D)
- Oval or Potato Shaped (E)
These pearls can appear to be round in photographs, or perceived as round when the untrained observer is looking at the actual pearl, but would not pass the "roll" test mentioned in the previous section. Many of these out-of-round pearls might also be classified in the Semi-baroque category.
Semi-baroque (F) is a general term that typically describes a wide variety of pearl shapes that are classified as neither round, nor off-round pearls, and would include the following eleven categories:
- Button Pearls
- Coin Pearls
- Drop Pearls
- Oval Pearls
- Peanut Pearls (Double Potato)
- Pear Pearls
- Rice Pearls
- Rondelle Pearls
- Stick Pearls
- Twin Pearls (Irregular Twins)
- Wheat (Firecracker) Pearls
Baroque is a general term that indicates a significant irregular pearl shape. Typically, these baroque pearls are the least expensive variety, yet certain exotic South-Sea or Tahitian specimens can be more valuable than perfectly round pearls from other regions. The baroque pearl can be abstract (asymmetrical) in its irregular shape, or it can resemble a stick, cross, or any number of other more "symmetrical" shapes.
Symmetrical Semi-Baroque Pearls
Oval pearls are narrower at the ends than they are in the center, and ovals are categorized as having a "symmetrical" shape. Button pearls (aka "coin pearls") are flattened, making them resemble a button or disk, rather than a perfect sphere. Button pearls are also categorized as symmetrical. Drop pearls are "pear" or "teardrop" shaped. These pearls make attractive earrings or pendants. They are also categorized as having a symmetrical shape.
Some baroque pearls develop with grooves or rings encircling them. These pearls are known as "ringed" or "circled" baroque pearls, and can resemble a lamp base or chair leg that is turned on a lathe. "Stick pearls" (aka "Biwa pearls") are elongated, flat, and narrow; and can be "center drilled" through the long dimension; or "top drilled" through one of the narrow ends. So-called "wheat pearls" (aka "firecracker pearls") are pear-shaped, with a larger and smaller end.
Mabe Pearls (aka "blister pearls") are half-round pearls that are flat on one side. When the nucleus or foreign matter becomes fixed to the inside shell wall rather than in the oyster's body tissue, only the exposed portion becomes covered by the oyster's pearl-sac resulting in a blister pearl. Mabe pearls are typically grown in Silver-lipped and 'Mabe winged' pearl oyster.
Mabe, baroque and off-round shapes have gained in popularity as the price of these irregular-shaped pearls have place them within the budget of a larger buying market. Additionally, the movement towards "natural" and/or "organic" consumer goods has also fueled growing interest in "imperfect" gems and pearls.