A pearl is a spherical structure consisting of calcium carbonate in crystalline form ( aragonite ) produced by the mantle of molluscs (typically oysters) as a response to the presence of foreign bodies that can damage the tissues. The word pearl comes from the Latin pernula , the name used to indicate the shell that contains it.
CLASSIFICATION OF PEARLS
Used a lot in jewelry, pearls are classified according to some criteria:
The size of the pearls is more important than the weight: expressed in millimeters, the greater their size , the greater the value of the pearls , especially exceeded 8-9 mm.
Pearls have an oval, pear or irregular round shape (the so-called “baroque” pearls ). The symmetrical ones are the most precious, the dimensions vary from 2 mm to 16 mm in diameter, the size depends on the type of mollusc in which they are formed.
The shine is the factor that makes it unique and distinguished compared to other gems. The shine is due to the light that penetrates through the various layers of mother-of-pearl and returns to the eye of the observer from the inner depths of the gem. The effect is that of a glow coming from within, from the very heart of the pearl.
Pearls that have a very thin layer have an opaque and dull appearance, as well as in the case of layers produced too quickly.
The sheen of the pearls is grouped into four categories
- Excellent (Eclatante): The reflections are bright, very clear and well defined
- Good: The reflections are bright, but slightly blurred at the ends
- Discrete: The reflections are weak, confused and blurred
- Poor: The reflections are very indistinct and widespread.
The pearls are available in various colors, from white to black. The natural color usually comes from a combination of several factors: the predominant base color, one or more colors that exceed the body color and also the play of bright colors, such as a combination of colors such as pink, green, blue or also silver, which changes when you move the pearls in your hand.
As for the other gems, the color of the pearl is formed by:
- Tint, that is the first perception that one has of color;
- Tone, ie the greater or lesser brightness of the color itself;
- Saturation, which represents its strength and intensity.
Pearls never reach the high saturation that other gems present, instead presenting a wide palette of soft hues.
Taking into account the background color, in the GIA system are recognized 19 shades of pearls divided as follows:
Neutral : white, gray and black;
Almost neutral : silver, cream and brown;
Tints : all other colors