The six most important elements to grading a pearl are:

Luster

If only one factor were to determine the worth of a pearl, luster would be the top consideration. As an expression of a pearl beauty, luster is determined by the amount of light reflected from the pearl surface as a combination of its outer brilliance and deep inner glow. The highest quality pearls with the best luster will reflect a clear mirror image of the objects around it. The closer to a mirror image you see, the better the luster. Pearls with fine luster also seem to glow warmly from within.

The thickness and quality of pearl nacre affects its overall luster. However, a thick nacre coating does not always guarantee that a pearl will have a high luster. Genetic imperfections in some oysters inhibit them from secreting nacre in perfect patterns that result in high luster. Generally, avoid any pearls that appear too white, dull, or chalky as you can be sure these are lower value pearls.
Remember to examine the luster of pearls under a fluorescent lamp and in front of a light colored or optimally white background.

Nacre Thickness
Pearl nacre is the natural coating a mollusk produces to protect itself from irritants such as shell fragments or in the case of a cultured pearl, an implanted bead nucleus. Pearl nacre is created by thousands upon thousands of layers of this crystalline substance technically known as calcium carbonate (CaCO3). This same radiant iridescent material is what lines the inner surface of oyster shells and is referred to as Mother of Pearl.

Nacre thickness is a very important factor in determining pearl quality in that it directly affects the durability and therefore, how long the beauty of a pearl lasts. Along with nacre thickness, nacre quality is further determined by how light reflects through the layers of the nacre and illuminates a pearl. Sometimes pearls with thick nacre fail to exhibit the intensity of luster that is expected due to the way in which the layers of the nacre crystallized. Oftentimes this has to do with environmental factors such as water temperature and stability of overall water conditions, which affect the speed at which the nacre is produced.

A few quick ways to evaluate nacre thickness is to look for uniform iridescence, intensity of luster, and cracks and peeling. Estimate thickness by observing the nacre at the drill hole. The most accurate way to determine nacre thickness is through x-ray done at a gem testing laboratory.

For Akoya Pearls, a minimum nacre thickness of 0.4mm is recommended to ensure that the pearls will last a lifetime. For South Sea Pearls and Tahitians, which typically have thicker nacre, a minimum of 0.8mm is recommended. In several countries where these pearls are cultured governments have imposed a minimum nacre thickness of 0.8mm to prohibit low quality pearls from being exported.

Surface Quality

Since pearls are a product of nature, there are imperfections such as bumps, chips, and scratches. The more flawless the surface of the pearl is, the higher it will be valued. However, a flawless pearl only comes about once in about every million, as pearls are the result of a natural process, and an oyster will usually leave some sort of unique mark on the finished pearl. As a product of nature, pearls are almost never flawless and small blemishes are common.
There are many types of surface characteristics which can be seen very easily or very subtly. They are divided into four classifications.

• Clean - pearls that contain no blemishes or ones that are very difficult to see even with a trained eye
• Lightly Blemished - pearls that show minor surface blemishes when examined by a trained eye
• Moderately Blemished - noticeable surface characteristics
• Heavily Blemished - obvious blemishes that will affect durability of the pearl

It is important to note the difference between damaging and non-damaging blemishes. A damaging blemish such as a crack worsens over time, while a non-damaging blemish such as a bump or spot remains the same over time. Damaging blemishes are obviously worse.

Color
Pearls are available in a fascinating array of colors from white to black and virtually every color in between. The choice of pearl color is important to consider based on preferences and cost, as well as the wearer skin, eye and hair color. When evaluating pearl color, it is important to note both body color and overtone. The body color refers to the basic color, while the overtone refers to the presence of a secondary color. For example, pearl with a white body color can posses a surface iridescence reflecting a cream overtone. Although pearl color choice is a personal preference, rose and white overtones are commonly preferred by women with fair skin, while cream and gold tone pearls are most flattering to those with darker complexions.

In addition to basic color, pearl color tone intensity is also evaluated. Darker toned pearls that are richer in color are highly desirable and costly when compared to lighter intensity color pearls.

Shape

Pearls develop into a variety of shapes. Round pearls are the rarest and command the highest prices. The term 'round' does not mean spherical like a marble but the pearls should not be obviously oval or flattened to the naked eye.

Very few pearls actually come out of an oyster perfectly round, which is why such pearls are the most rare and valuable. With many shapes available, pearls are first divided into three shape categories: symmetrical, spherical, and baroque. Within these categories, they are further defined by unique shapes such as teardrop, button, pear-shape, coin, flat, rice, oval, and cross just to name a few. Spherical pearls are by far considered the highest quality, although symmetrical pearls including pear and teardrop shape, along with baroque pearls are gaining more popularity due to their unique shapes and lower costs.

Size

The size of a pearl is measured across its diameter and its range can be smaller than 1mm to as large as 20mm or more. Not as an indicator of quality but rather the value of the pearl, size affects a pearl price. The reason why larger pearls cost more is very simple in that it takes more time and risk to cultivate a larger size quality pearl. Sizes vary depending upon the type of pearl: freshwater pearls typically range in size from 3 to 8mm, Akoya Pearls range from 3.5 to 10mm, and South Sea Pearls including Tahitians Pearls range from 10 to 18mm. The average and most popular pearl size sold today is 7 to 7.5mm, a good balance between size and cost.

Baroque and Drop pearls are measured through their width not their length. It is often difficult to decide on the correct size to buy someone and sometimes it might be a better choice to nest three smaller strands then to buy one large one.

Pearl Grading System

There is no international standard for grading pearls. One supplier's AA grade maybe another's A or AAA. To simplify and best represent the standard factors of pearl grading (luster, nacre thickness, surface perfection, color, shape, size), the Pearl Amor grading system accurately and consistently categorizes these 6 important factors by three individual grade labels. Along with the three major categories (AAA, AA, A) there are also two sub grades (AA+, A+), wherein the + represents a slightly less blemished surface.

AAA Pearl Grade

• . Luster: High/Intense with an exceptional mirror-like quality
• . Nacre Thickness: Very thick, with a minimum of 0.5mm thickness for Akoya Pearls
• . Surface Quality: Clean and virtually flawless
• . Color: Varied colors with sharp and distinct overtones
• . Shape: Perfectly round
• . Size: Varied

• . Luster: High with a clear reflection
• . Nacre Thickness: Thick, with a minimum of 0.4mm thickness for Akoya Pearls
• . Surface Quality: Slightly blemished with minimum 90% clean surface
• . Color: Varied colors with good overtones
• . Shape: Round
• . Size: Varied

• . Luster: Medium with a slightly dull reflection
• . Nacre Thickness: Medium to thin with a nacre thickness 0.3mm or less
• . Surface Perfection: Blemished with minimum 75% clean surface
• . Color: Varied colors with minimal to no overtone
• . Shape: Near round to off round
• . Size: Varied