This is a question we are often asked. There are many different types of pearl, some rarer than others, but before we start differentiating between them lets first understand how pearls are formed. Pearls are the product of the act of self-preservation by a mollusc, be it an oyster or a mussel. If the mollusc does not react in this way it will die.
In other words the creation of a pearl is caused by the protective reaction of an oyster or mussel to the accidental or deliberate introduction of a foreign body into its organism. This reaction starts by the mollusc covering the intruder with epithelial cells which will form a pearl sac around the intruder, which in turn deposit concentric layers of nacre that surround the offending object and slowly form the pearl, layer by layer.
So ...what is nacre?
Nacre is made up of calcium carbonate in the shape of tiny crystals called Aragonite. Calcium carbonate is also found in chalk, our teeth and various other everyday items. With a pearl the Aragonite crystals are held together with a glue-like protein called Conchiolin. In our teeth which are also made of calcium carbonate; the protein that holds that Calcium Carbonate of our teeth together is stronger than Conchiolin hence when we are invited to “test” the genuineness of pearls against our teeth it is not only unhygienic but totally undesirable as our teeth will scratch the pearl.
What makes nacre?
Epithelial cells produce nacre and are therefore essential to pearl formation. They are found in a special tissue called the mantle which is found at the hinge and the edge of the molluscs flesh, as seen in the photograph shown. Nacre grows not only on pearls but also as mother of pearl on the interior of the shell. Nacre layers within the shell of the mollusc act as a protective shield against the outside world, making the mollusc less attractive as food to predators. The only difference between pearls and mother of pearl is that in a pearl the layers are concentric and in mother of pearl they are flat or straight.
Epithelial cells produce nacre and are therefore essential to pearl formation. They are found in a special tissue called the mantle which is found at the hinge and the edge of the molluscs flesh, as seen in the photograph shown. Nacre grows not only on pearls but also as mother of pearl on the interior of the shell. Nacre layers within the shell of the mollusc act as a protective shield against the outside world, making the mollusc less attractive as food to predators. The only difference between pearls and mother of pearl is that in a pearl the layers are concentric and in mother of pearl they are flat or straight.
Where does a pearl gets its lustre from?
Nacre layers play a vital role in the pearl's lustre. Nacre layers are very thin, translucent and reflect light, thus creating the pearl’s distinctive lustre. Generally the thicker the nacre with regular, thin and translucent layers, the finer the lustre will be on the pearl. In other words lustre is caused by the reflection of light on the surface of the pearl and the refraction of light as it passes through the layers of nacre. This effect appears to make the pearl glow from within.
