Pearl Color

Pearl’s color description is divided into two parts: Body color and Overtone.

Body Color

Pearls’ body color can be broadly classified as white, pink, yellow, grey, bronze, green and black. In addition, the orient itself may show delicate but predomination hints of pink, yellow, green or blue. Many theories have been advanced regarding the causes of color in grey and black pearls. These include the presence of certain minerals and proteins in the water in which the oysters have developed, and the existence of a conchiolin-rich layer near to the surface of the pearls.

The color of pearls changes with the light source under which they are viewed; white light is preferred for color grading. When us daylight, the best results will be obtained under the light of a slightly overcast northern sky of medium latitude at noon. The direct sunlight should be avoided.

A thick conchiolin core or thick conchiolin rings within a pearl can create a dark brown to grey and blue color. The colors of a pearl usually resemble those on the inside of the shells. While shells regularly consist of a conchiolin layer, a prismatic layer and a mother-of-pearl layer, pearls tend to show a more haphazard combination of these layers.

The fine color of a pearl depends on the type and thickness of the prismatic and nacreous layers, in which conchiolin is the organic matrix. Colored pearls either have distinctly dark colors like brown, reddish-brown, grey and black or tints of these colors, which may appear as yellow, golden, bronze, green or orange hues.

According to the Uroporphyrine I, the porphyrine pigment that causes the dark color of both the shells and the pearls of Pinctada margaritifera and Pteria penguin, while the term conchporphyrine had at first been coined in the nineteen thirties. Porphyrines are usually found together with other water-soluble pigments, but they are not found in freshwater mussels. Porphyrines can bond with metals to form metalloporphyrines, and they are responsible for the red fluorescence of dark pearls under ultraviolet light.

Trace elements can also produce color, they have already been mentioned. They are either deposited in the conchiolin substance, or they replace atoms within the lattices of aragonite or calcite crystals.

Once the body color is determined, and then can concentrate on overtones, which are visible in a distinct circle on the surface of the pearls.

Overtone

Overtone is the presence of an additional color on a pearl or pearl product, usually pink, gold, green, or blue.

The phenomenon is dependent on the angle at which light rays strike the pearl and the direction from which the observer views the pearls.

The iridescence effect is usually seen as an overtone in pearl, which appears to float like a small circle on the surface of the pearl. It is made up of one, two or three nearly transparent colors, usually pink, blue and green, which stretch flatly over the circle. The combination of a pink and blue overtone appears slightly purplish and it is this combination that is valued most highly.

The overtone is rarely made up of more than 3 colors; they depend on nacre thickness and size. When a fine play of color is visible just on top or just below the surface, the overtone is called orient. Orient is only seen in Akoya culture pearls, where it may appear both alone or in combination with an overtone. Orient is more characteristic for natural pearls.

In the case of natural pearls, the effect of orient is due to a number if interchanging actions of light on the surface of a pearl. As the surface of pearls is curved, iridescent color can be observed from all directions.

Orient is usually attributed to a combination of two effects: interference of light on the layered structure of the upper part of a pearl and diffraction of light on the linear relief structure of the surface.

The layered structure is caused by thin, alternating layers of aragonite and conchiolin while the linear relief structure is due to the terrace-like arrangement of the edges of aragonite platelets and the grooves between them, which are filled with an organic membrane.