Mother of Pearl, also known as nacre, is the iridescent substance that lines the inner shell of certain mollusks, such as oysters, abalones, and mussels. Valued for its unique luster and shifting colors, its appearance definitively changes over time. These alterations result from reactions between its organic and inorganic components and various external chemical or environmental factors, rather than natural aging alone.
The Structure of Mother of Pearl and Its Iridescence
Mother of Pearl is a biocomposite material made of organic and inorganic components arranged in a highly ordered structure. Its primary constituent, making up about 95% of its weight, is aragonite, a crystalline form of calcium carbonate. These microscopic, hexagonal aragonite platelets are stacked like tiny bricks in a wall.
The remaining 5% is an organic protein matrix, primarily conchiolin, which acts as a flexible mortar cementing the aragonite layers together. This layered arrangement provides the material’s strength. The distinctive, rainbow-like sheen, called iridescence or “orient,” is not caused by pigment. Instead, it results from the physical interaction of light with the structure, where light waves interfere as they reflect off the numerous thin aragonite layers.
Environmental Factors Causing Color Changes
The combination of aragonite and conchiolin makes Mother of Pearl vulnerable to two primary types of environmental degradation. The most immediate threat is chemical exposure that dissolves the inorganic calcium carbonate. Acids, even mild ones like those found in vinegar, citrus juices, or wine, react with the aragonite, causing decomposition.
This reaction etches the nacre surface, leading to a loss of the precise layered structure necessary for iridescence. The result is a dull, chalky appearance and a permanent loss of luster. Even human perspiration, which contains mild acids and salts, can slowly degrade the surface if not regularly wiped away.
The second type of change involves the organic conchiolin matrix, which is susceptible to thermal and light damage. Prolonged exposure to intense ultraviolet (UV) light, such as direct sunlight, or high heat degrades this protein component. This degradation causes the Mother of Pearl to yellow or darken over time, losing its clean, bright appearance.
Mother of Pearl naturally contains trace amounts of water within its structure. Exposure to extremely dry conditions or high heat causes this moisture to evaporate. When the material dehydrates, the organic matrix becomes brittle, leading to hairline cracking or fissuring in the nacre layer and diminishing its luster.
Maintenance Practices to Preserve Appearance
Maintaining the original color and luster of Mother of Pearl requires preventative care. Because of its sensitivity to acids, treat it similarly to pearls: ensure it is the last item put on and the first taken off. Contact with cosmetics, perfumes, hairspray, and household cleaning chemicals must be avoided.
After wearing, gently wipe the surface with a soft, lint-free cloth to remove residues like perspiration and body oils that could etch the surface. For cleaning, use only a soft cloth dampened with lukewarm water and a mild, non-detergent soap. Harsh cleaners, abrasive materials, and ultrasonic or steam cleaners must be avoided, as they damage the delicate nacre layers or the organic cement.
Proper storage is crucial to prevent heat and dehydration damage. Mother of Pearl should be kept away from direct sunlight, radiators, or hot environments. It is best stored in a separate, soft pouch or a fabric-lined jewelry box to prevent scratching. Avoiding excessively dry environments, such as prolonged storage in a safety deposit box, helps preserve the internal moisture content and safeguard the material’s luster.