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Pearls stand apart from other gemstones. While most are mined from the earth, pearls are produced by sea and freshwater mollusks. Many jewels are transparent enough to facet, and may be cut to better display their internal color and clarity characteristics. While pearls reflect and diffuse light through their upper layers, they are usually left in their original shape.

The four Cs of cut, color clarity and carat are helpful for assessing the value of most jewels. Though one can evaluate a pearl by its color and size, cut and clarity are not as compatible. To better determine the quality of pearls and pearl jewelry, the Gemological Institute of America (GIA) developed the Pearl Description System in 1998. This system names seven value factors to keep in mind when evaluating pearls, size, shape, color, luster, surface quality, nacre quality and matching.

Depending on the type of pearl and jewelry design, some factors may have more of an impact than another. For a brooch with a single pearl, matching may not be so critical. Some pearl types may place a greater emphasis on color, others may place a greater value on size or shape. Quality factors by themselves are important, though how they balance with one another also matters.

 

Size
Pearl size is mostly determined by two factors: the dimensions of the implanted nucleus and the thickness of the nacre that grows layer upon layer around the nucleus. Large cultured pearls that lack nacre thickness have low value, due to dullness and a higher likelihood of discoloration and cracking, while a pearl with a thick nacre coating will retain its luster and beauty for a lifetime when properly cared for. If all other qualities are equal, larger pearls will fetch a higher value. Sizes are generally measured in millimeters, rounded to the nearest half millimeter.  They’re available in sizes as small as 2mm, to over 15mm. If a pearl is round, it’s measured by diameter. Other pearls, like drop or baroque shaped, are measured by length and width. As with other jewels, the larger the pearl, the rarer they become. With other factors being equal, a 10mm pearl will fetch a higher price than an 8mm one.

 

Shape
Pearls are categorized into shapes known as Round, Near-Round, Oval, Button (circular and flat, like a disc,) Drop (pear shaped,) Baroque (irregular) and Semi-Baroque. Additionally, pearls of any shape may have ridges along their surface, a phenomenon known as circled pearls.

Perfectly round cultured pearls are the rarest and most valuable.  Although most cultured pearls are almost round, only about 1% are perfectly spherical. To check a strand for roundness, roll it across a flat surface to see if it moves in a smooth and even fashion.

As mentioned above, round pearls are those that are spherical in shape. Perfectly round pearls are the rarest shape, tricky to produce. While bead nuclei can be shaped into spheres, mollusks may deposit nacre on the bead unevenly, creating a different shape than intended. Near round pearls are those that appear almost, but quite round to the naked eye. Circled pearls should not be confused for round or near round. Circling refers to grooves or ridges that ring the gemstone, and can occur on any shape.

Other symmetrical pearls include ovals, which are round and oblong. Drop pearls resemble ovals, with one end narrower than the other. This type is popular for pendants and earrings. Some of the most famous pearls in the world, such as La Peregrina, are drop shaped. Button pearls look like circles when viewed from above or below. From the side, they have dome shaped tops and flattened bottoms.

Semi baroque pearls have subtle irregular shapes, such as an asymmetrical drop with a wavy surface. Baroque pearls have a more dramatic appearance. Many designers take advantage of baroque pearls’ unusual appearances to create fanciful settings, with these pearls serving as the petals of a flower, a merman’s torso or the skirt of a dancing girl.

There are pearls that don’t fit into the seven categories above. In these instances, GIA recommends describing the shapes. These can include coin pearls, which are circular but flat on top and below. Bars are oblong and can resemble cylinders with tapered ends. More whimsical forms can be deliberately cultured. Depending on the shape of the nucleus bead, cultivators can create pearls shaped like crosses or stars.

 

Luster
Luster refers to how light plays off of the surface of a pearl, imbuing it with the jewel’s distinctive shine and beauty. When checking pearls for luster, view them while standing with your back to a source of light. The brighter and sharper your reflection on the surface of the pearl, the stronger the luster.

The layers of nacre that make of a pearl are translucent. When light travels through them and reflects back to the eye, luster occurs. The way a pearl shines helps make it distinct from other jewels, and is part of what makes pearls so desired. Pearl cultivators strive to give their mollusks cool stress free environments to encourage higher luster.

GIA divides luster quality into five classifications. Excellent luster is bright with clearly defined reflections. Very Good shines just as much as Excellent, though the reflections are not as distinct. Pearls with Good luster has the brightness of the previous two, with blurry edged reflections. Fair luster has a low shine with indistinct reflections, and Poor is dim with dispersed light.


Color
Pearls come in a variety of shades, with the major classifications being white, pink, silver, cream, gold, and black. These tones are further divided into bodycolor, which is the dominant hue, the translucent shade that plays across the surface of a pearl known as overtone, and orient, the name for the blend of colors gleaming just below a pearl’s surface. All pearls in a strand should be consistent in color.

While most colored gemstones have their colors categorized by hue, tone and saturation, pearls are graded by a different system. The layers of a pearl’s nacre scatter light, creating a soft appearance, low saturation, and splitting white light in unusual ways. Together, bodycolor, overtone and orient make up a pearl’s color.

“Bodycolor” refers to the major hue of a pearl. Whereas some pearls may have overtone or orient, bodycolor apply to all pearls. When placed on the market, pearls may receive romantic names to describe their bodycolor, such as champagne or peacock. What may appear champagne colored to one person might look golden to another, or two different names may refer to the same color.

To reduce confusion, the GIA established several hue categories for their Pearl Description System. Neutral colored pearls are white, grey and black. Near-neutrals are cream, silver or brown tinged. “Hues” are for pearls that don’t fall into the other classifications. These are referenced on a hue wheel which recognizes nineteen different colors, with names like “purple” or “reddish purple” to help give a clear idea of a pearl’s hue.

Orient happens when a pearl’s surface scatters white light into the colors of the rainbow. When it appears, it indicates a thick layer of high quality nacre. A pearl’s overtone is one or more translucent secondary hues overlaid upon the bodycolor. They form at the edges of overlapping nacre plates, deflecting light. Some overtone and bodycolor combinations, such as pink over white or purple over blue-grey are in high demand.

 

Surface Quality
This term refers to the absence of disfiguring irregularities such as minor color variations, bubbles on the pearl’s exterior or abrasions that affect the luster or color of the jewel on the surface of a pearl.  The fewer the blemishes, the more desirable a pearl becomes.

As with other gemstones, very few pearls are flawless. More often, they possess quirks known as surface characteristics. These can include tiny flat patches, wrinkles, scratches or other qualities that may influence the beauty of a pearl. Though some characteristics are severe enough to weaken a pearl’s durability, others can be concealed through careful mounting or placement of a drill hole for stringing.

GIA recognizes four levels of pearl surface quality. Clean pearls have no surface characteristics, or are so minute, they’re barely detectable by trained professionals. Clean pearls have the rarest surface quality. Lightly spotted pearls have small quirks that are located by experienced eyes. Moderately spotted pearls have characteristics more apparent to the naked eye, and heavily spotted pearls have surface quirks which may influence their durability.

 

Nacre Quality
When evaluating a pearl’s nacre, there are four aspects to examine. Ideal nacre should have many layers over the nucleus and remain translucent. The nacre should be evenly deposited and aligned just so. Together, these elements can create a pearl that has beautiful luster as well as durability.

Nacre can look its best when it has a long period of time to form around a pearl. This allows for extra nacre to form around the nucleus, forming a larger pearl with many layers of nacre. However, more nacre does not necessarily make the best pearl. It can deposit unevenly, impacting how light reflects off of the jewel and how light shines through the pearl. The more time nacre has to form against the nucleus also increases the likelihood that the pearl will be a shape other than the popular round or near round.

When layers of nacre are stacked neatly on top of one another like pages in a book, light is able to travel deeper into a pearl, giving it the desired translucence. Aligned nacre is more likely to have mirror like shine and sharp reflections. If nacre is less organized, light diffuses among the layers, creating a softer luster.

 

Matching
Some pieces of jewelry blend pearls of different colors, shapes and sizes to catch the eye. Many others reach for a uniform effect with their pearls. In these instances, the jewels should be as similar to one another as possible, assessed by the quality factors listed above.

Matching is a unique quality factor in that it only applies for certain designs. Pieces that feature only one pearl don’t have to worry how well the jewel coordinates with its companions. For other styles, matching takes the factors of size, shape, color, luster surface and nacre quality to determine which pearls will make a piece look harmonious.

No two pearls are exactly the same, making matching a challenge. For example, if a jeweler wants pearls for a necklace, a sorter must begin with a large quantity of pearls. First they organize by obvious characteristics, such as round from baroque, or white from golden. As the remaining piles grow smaller, pearls are categorized by subtle details, such as the intensity of overtone. The end result should be a set of pearls that look uniform in all but the closest scrutiny.

Even when the pearls are meant to be different, like a graduated strand or multicolored piece, matching matters. In these circumstances, to match is to find pearls that make a visually appealing whole. That may mean seeking out jewels with contrasting cool based colors or pearls that are of similar quality but in a range of sizes.

GIA names four categories for pearl matching. Excellent matching features pearls that appear uniform. If they are drilled for stringing, the hole is centered on the jewel. Very Good matches have subtle variations between pearls, and Good matches feature small differences among the pearls. Fair matches have noticeable variations between the pearls that are unintentional.

Follow this link for some interesting videos on the Secret Life of Pearls

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