A quote by Susan Young goes like this – “As a pearl is formed and its layers grow, a rich iridescence begins to glow. The oyster has taken what was at first an irritation and intrusion and uses it to enrich its value.” Pearls have been of great value since ages, in adorning oneself and to embellish several anecdotes. But how did the pearl come to be?
When you step into a jewellery shop and look at the display of all things in ‘pearl’, little do you realise that the shiny, polished beads are a product and creation of rather ordinary, yet unique-looking oysters floating somewhere in the oceans. Pearls are the result of a biological process – the oyster’s attempt to protect itself from foreign bodies.
Oysters, shelled mollusks of the sea, are bivalves, meaning that their shells are made of two parts, or valves. The walls of these shells are held together by an elastic ligament, which is positioned where the valves come together. They keep the valves open so the oyster can eat. Like any other sea creature, oysters also possess a heart, stomach, intestines, gills, mantle and a mouth. When the oyster grows in size, its shell also grows. The growth happens when new materials are added to the edges of the shell by the mantle. The mantle is a thin layer of tissue that lines the inner parts of the oyster’s shell. The mantle possesses glands that extract minerals from the water and convert them into building blocks on its hard shell.
The oyster’s shell (exoskeleton) has three different layers. The outermost layer is called outer proteinaceous periosteum. The middle layer is called prismatic layer and the innermost later is known as nacre layer, i.e. the layer that lines the shell’s insides. This nacre layer is also known as the ‘pearl layer’, owing to its iridescent, light-reflectiveness. Considering its role in forming the pearl, an oyster is also called “the mother of the pearl”.
The formation of a pearl begins when a foreign particle slips into the oyster between the mantle and the shell and irritates it. The oyster, to cover up the irritant, protects itself by encapsulating the interloper. The mantle covers the irritant with layers of the nacre substance, and thereby, these layers of nacre eventually work to convert the foreign particle into a pearl.
However, the nacre layers are incredibly thin. It takes an oyster around 24 months to make a natural pearl that is 5 mm in diameter. Farmers who harvest oyster pearls, carry out the process carefully through a small incision. They tend to use an oyster repeatedly for harvesting pearls. While many people believe that oysters die when the pearls are taken out, they do not generally lose their life if harvested with care.