Luster is widely considered the most important factor in judging a pearls quality. It is the term used to describe the reflectivity of the pearls surface. The higher the pearls luster is, the more it shines, reflecting light and objects more clearly. For a pearl to have a deep mirror-like reflection, it must have a very smooth surface created by many even layers of nacre. Saltwater pearls generally have higher luster than freshwater pearls. Pearls with low luster appear dull or chalky white, instead of brilliant and shiny.
The second most important indication of a pearl’s value is the thickness of coating. A pearl is made up of layers and layers of a substance called nacre – calcium carbonate and protein. The thicker the nacre is, the more durable and valuable the pearl. The average thickness of a pearl’s nacre ranges from 1mm to 3mm. Coating cannot be easily judged by an unpracticed eye, but can be determined by how long a pearl has been underwater.
Generally, as the size of the pearl goes up, the value goes up as well (all other factors being equal.) The standard way pearl sizes are measured is in millimeters (mm). Pearl sizes can range from 1mm (or even less for some seed pearls) up to as large as 20mm for large South Sea Pearls. Large sized pearls are rare, and size has a significant effect on price. A difference of one millimeter can raise the price by a 100 to 200 per cent in the pearl industry. Below is a list of the most common size ranges for the different types of cultured pearls.
Tahitian Pearls: 8mm to 17mm
White and Golden South Sea Pearl: 9mm to 18mm
Akoya Pearl: 2mm to 10mm
Freshwater Pearl: 2mm to 15mm
Round - Perfectly round pearls are the most sought after and the rarest of cultured pearls. Because of their rarity and "classic pearl" appeal, they are typically the most highly valued of the pearl shapes. Generally all pearls are nucleated with a round bead in the hopes of culturing a round pearl, but only 5-10% of a pearl farm's harvest will actually result in a pearl that can be qualified as round.
Near-Round - To the untrained eye, near-round pearls have the appearance of being perfectly round pearls, even more so when worn on in a necklace. If the pearls are not perfectly round but very close to round they are considered “near-round” or sometimes called “off-round”. The majority of freshwater pearls on the market will fall into this category.
Button – Button pearls are symmetrical in shape and have a round appearance from the front, with the opposite side being flat. While noticeable when strung as a strand, their button shape can appear as round when set as studs or cufflinks, and are considerably less expensive than round pearls.
Oval – Oval pearls are symmetrical but not perfectly spherical. Oval pearls have the appearance of an elongated round pearl and are considerably less expensive than round pearls. Oval pearls have their widest diameter found at the center of the pearl.
Drop – Drop pearls are symmetrical in shape and have a tear-drop appearance. They are similar to ovals but have one end noticeably thinner than the other, sometimes coming to a distinct point. A pearl that has a perfect "pear-shape" can be very valuable, especially in larger sizes, and may even fetch higher prices than rounds.
Baroque – Baroque pearls are non-symmetrical and have no specific shape designations except for the fact that their shape is irregular. Their shapes can vary from off-round to pebble-shaped to irregular drop shapes. The demand for baroque pearls has steadily increased as more and more consumers and designers gain appreciation for the wide range of unique shapes found in baroque pearls.
Circle - Circle pearls can have a variety of different shapes including baroque, drop, button and near-round. The defining characteristic that designates a pearl as circle is the presence of visible concentric “circles” or “rings” around the diameter of the pearl. Circle pearls are most often found in South Sea and Tahitian Pearls, and are gaining popularity due to their unique appearance and affordability.
Pearls are the only organically created gem. Because they are produced by a living creature, tiny surface imperfections are almost always present. The fewer and smaller these imperfections, to more valuable the pearl will be. The size of the pearl should also be taken into account when examining surface blemishes. A larger pearls value will be less affected by small imperfections. Blemish location can also be a factor because if the imperfections are concentrated in one area they won’t be as noticeable as blemishes that are spread out over the pearls surface. Blemishes are also less noticeable if the pearl has high luster.
Pearls come in a wide variety of natural colors. Basic colors include cream, white, gray, green and pink. A pearls color does not affect its value or quality grade as much as other factors. The most important aspects of a pearls color, in relation to judging its quality, are the saturation and even distribution of its color. While color demand is primarily based on personal preference, rare and intense fancy colors are often sold at a premium.