Whenever we think of pearl jewelry, the first thing that comes to mind is luster. However, what most people don’t realize is that the radiance of a pearl’s luster depends entirely upon the quality of its nacre. In fact, it won’t be wrong to say that the value of a pearl depends to a large extent upon nacre quality.
Nacre, also known as mother-of-pearl, quite simply is what makes a pearl, a pearl. It is the silky, shiny and iridescent material we see on the surface of pearls as well as on the inner sides of the shells of pearl forming oysters.
Nacre is formed in concentric layers around the bead nucleus of a cultured pearl. Chemically, nacre is made up of aragonite and conchiolin. Both these substances are created by the oyster.
Aragonite is a form of calcium carbonate that is crystalline in nature, with the crystals being hexagonal in shape. Conchiolin is a binding or glue-like substance which acts as an adhesive to bind the different layers of aragonite together.
Left to right: Akoya Pearl Stud Earrings, 6.5 - 7.0 mm, Pearls of Joy; Cross Section of an Akoya Pearl, Pearls of Joy
In the case of cultured pearls, conchiolin is the first layer deposited by the oyster on the bead nucleus or ‘irritant’ introduced into an oyster for growing a pearl. On this initial layer of conchiolin, the oyster deposits an exceptionally thin layer of aragonite crystals, arranged like a wall with hexagonal bricks. The aragonite layer is followed by another layer of conchiolin, thus creating nacre.
Layer upon layer of nacre is deposited on the bead nucleus. The oyster continuously performs this process. Eventually, when enough layers have been created, a glossy, luminous cultured pearl is formed.
Different types of cultured pearls have different nacre thicknesses. For instance, for top quality Hanadama Akoya pearls, the minimum required nacre thickness is 0.4mm. By contrast, top quality South Sea pearls will have an overall nacre thickness measuring between 2.0 mm to 4.0 mm.
Nacre is a strong material that has immense tensile strength, such that it can take a lot of stress without breaking or chipping. In addition, it is a lightweight, highly reflective material, with superb optical properties, and it gives pearls their unique beauty.
Nacre quality can be understood through three simple categories:
The nacre is thick and evenly layered. The bead nucleus is not visible but a slight ‘blink’ (glimpse of the nucleus) from some angles is ok.
The nacre is not thick so that there is strong ‘blinking’ especially when the pearl is rotated and light hits it at different angles.
The pearl is dull and without any radiance. The nacre is quite thin or may not have developed properly on these pearls.
Pearls with thin nacre are lifeless and unattractive in appearance. They are also not very durable. In fact, it’s quite possible for such low quality pearls to chip or break. Pearls with thick nacre have a silky or satiny look and appear bright and radiant. It's not easy to chip their highly iridescent nacre.
Traditionally cultured freshwater pearls (which are cultivated through the insertion of a piece of mantle tissue), are all nacre. By contrast, Edison type Freshwater pearls and all saltwater pearls are bead-nucleated pearls, with nacre layers forming an iridescent coating on the bead nucleus. In both cases, pearls with thick, strong nacre will continue to look beautiful for years and years.
The thickness of nacre also depends on how long the oyster has been left in water, with longer times leading to thicker nacre and richly lustrous pearls.
At reputable pearl sellers, like Pearls of Joy, you will only find high quality pearls which feature consistently thick and superior nacre.
Nacre helps determine the color of the pearls. This is because color pigments are present in the conchiolin layers which in turn lend the pearl its body color (the aragonite crystals are usually transparent).
For instance, white South Sea pearls have an almost colorless to light grey or beige colored conchiolin while for golden South Sea pearls, the color of the conchiolin can range from orange, brown to reddish brown, giving these pearls their distinctive light gold, champagne or deep gold colors.
(In addition, some trace element compounds, such as iron and magnesium, present in the water around pearl farms also affect the body color of the pearl.)
Nacre layers are actually translucent, which allows light to reflect or bounce back off the surface of pearls. This creates luster. Thick nacre, or more layers of nacre, results in sharp and strong luster, while thin nacre makes for dull and lifeless looking pearl.
Since nacre is translucent, light can actually penetrate through some of its layers, and when it bounces back, it splits or diffuses into the colors of the rainbow. This interaction between nacre and light creates iridescence, which is the shiny display of color that changes when a pearl is rotated.
One of the best types of pearls to observe this diffusion of light is the Tahitian pearl. The secondary colors or overtones of these pearls can range in hues from green, blue, cherry, aubergine and the much- coveted peacock tones. This magnificent array of secondary colors is only possible because of the way light separates when bouncing back from the inner layers of the Tahitian pearl's nacre.
Nacre adds so much to a pearl’s beauty. The difference between thin and thick nacre is like the difference between day and night. Pearls with thick nacre have bright and lustrous surfaces and look radiant.
At Pearls of Joy, you are guaranteed to find stunning, luminous pearls with thick nacre, that will give you joy for years to come.
Featured Image: Hanadama Akoya Necklace 8.5 - 9.0 mm, Pearls of Joy