The magnificent silky luster of pearls attracted the attention of people for centuries. A pearl possesses the several attributes that make it valuable, however, its pleasant luster is the most valuable of them.
Causes of origin of the luster of Pearls
First of all, the luster of Pearls depends on the origin of the mollusk, thus the so-called Oriental mollusks contain the most splendid pearls inside them, in regards to their luster. Thus, the oriental pearls are more valuable.
Each shell contains thin layers of carbonate of lime, that are forming a pearl. These layers of nacre follow the shape of the mollusk.
Nacre is a very curious substance in itself. It contains the numerous iridescent layers, whose curved edges are sparkle so attractively. Their genuine splendor could be easily observed under the microscope. Exactly these curved edges, located in the variety of layers, are causing this splendid luster, that is similar to the rainbow.
Physicists call this effect, or an optical illusion, if you like — the “phenomenon of interference.”
The phenomenon of interference, according to physicists, signifies the moment, when the waves or the rays of light, in our case, after being bent or reflected, overlap each other. More accurately, this effect is called an “interference pattern.” The phenomenon of interference has been simultaneously discovered by Robert Boyle and Robert Hooke, by the way.
The structure of a Shell, which is the cause of a pearl’s luster
Luster is caused by the structure of the shell, as well. A pearl is formed by concentric layers, where the each consequent layer surrounds of the previous one.
The shell consists of 3 types of layers:
- the “conchiolin epidermis” — a mantle of mollusk;
- the inner prismatic formation;
- the “mother-of-pearl” or “nacre.”
The mollusk uses only the third type of layers in forming the lining of the shell. Exactly the same matter the mollusk uses in forming of a pearl.
This layer, called “nacre” is composed of ultra thin strata of wavy shape, which overlap each others and thus cause a pearl’s luster, as was described above.
However, these layers are not regular, they possess different thickness and shape. They produce a pearl, as though, a pearl was wrapped up in them. This peculiarity is the cause of the irregular shape of the pearls, as well. Thus we observe the pear pearls, button pearls and other baroque varieties of pearls.
Well formed pearl — the best luster
Properly formed pearl has the shape of a perfect sphere. A pearl could acquire this shape, thanks to the properly formed structure of layers. An ideal structure of layers is similar to the structure of an onion.
When a pearl is formed this way, it is able to properly reflect the rays of light and to possess the phenomenon of interference in the sufficient degree. Due to the proper structure, a ray of light is reflected in the right direction and bent under the proper angle, that facilitates a splendid luster of a pearl.
Any perfectly round pearl is the most valuable not only because of its shape. A round shape of a pearl signifies the proper formation of a pearl inside the shell, whereupon a pearl contains well formed layers inside it, which in turn have been formed of nacre, the only layer, that a shell is used in the process of pearl’s forming.
Thus, well formed pearl possesses the shape of regular sphere, which helped it to reflect the rays of light in the right way, that, in turn, cause an effect known as the phenomenon of interference. Where the phenomenon of interference causes a natural luster of a pearl.