Pearls are categorized and sorted based on 8 quality and valuation factors: size, shape, color, nacre, luster, orient, surface and coherence.
Most pearls are measured by their diameter; though, irregularly shaped baroque pearls are measured by their width and occasionally, length. The standard unit of measure is the millimeter.
From 1 millimeter to over 20 millimeters, the size of a cultured pearl depends on several factors. These factors include the size of the parent mollusk, the size of the implanted nucleus and the length of cultivation. All other factors equal: the larger the pearl, the greater its value.
Pearls come in an infinite variety of shapes, partially determined by the shape of the nucleus around which the pearl is formed. Round pearls are the traditional favorite.
No matter the shape, a pearl falls into one of four main categories:
Round: symmetrical spheres
Semi-Round: spherical oval, pear-shape and teardrop
Circled: streaks, ridges or rings in regular formation on the upper third (minimum) of the pearl's surface
From opaline white to anthracite black, the palest pastels to vibrant hues, pearls come in almost every color and shade. The finest pearls have a subtle interplay of colors, the primary body color plus delicate overtones. The rarest color is the gold of the golden South Sea Pearl.
While color of pearl is really a matter of the wearer's preference, rose or silver/white pearls tend to look best on fair skins while cream and gold-toned pearls flatter darker complexions.
A pearl and the inside surface of its parent mollusk are made of nacre. Nacre is the crystalline substance that, layer by layer, builds up around the small bead or piece of shell (the nucleus) that is implanted during the culturing process.
The thicker the nacre, the more lustrous and durable the pearl. When seen through a microscope, the surface nacre of a pearl looks like a lunar landscape. Each pearl's surface has irregular and distinct 'fingerprints' that are unique.
Pearls have a rich, inner glow that seems to come from deep within — that's luster!
Luster is an effect caused by light reflecting an diffusing through layers of nacre. High luster tends to make a pearl more valuable. The luster of a good quality pearl should be bright not dull. You should be able to see your own reflection clearly on the surface of a pearl. Any pearl that appears too white, dull or chalky, indicates low quality.
The play of light refracted through many layers of concentric nacre creates orient, the iridescence of a pearl that sometimes creates a rainbow effect. The Latin word oriens means 'the rising of the sun.'
'Cleanliness' affects the value of a pearl. Generally, the fewer blemishes on the pearl, the better. Tiny irregularities are acceptable and can be a test of authenticity.
Each pearl is unique. In order to create jewelry, pearls that complement or match each other are selected in a process that may take years. Thousands of pearls may be rejected to find the desired combination. When results are successful, the piece works as a harmonious whole — it has coherence, balance.