mother-of-pearl

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mollusk shells
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mother of pearl
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crustacean shells
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Nacre, also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer. It is strong, resilient, and iridescent. For more information on shell structure see: Mollusc shell.

This substance is called "mother of pearl" because it is literally the "mother", or creator, of true pearls.

Nacre is found in certain ancient lineages of bivalves, gastropods and cephalopods. However, the inner-shell layer in the great majority of shelled mollusks is porcellaneous and non-nacreous, frequently resulting in a non-iridescent shine like that of a porcelain plate or, in some species, presenting non-nacreous iridescent effects such as 'flame structure' (e.g. conch pearl).

Pearls and the inside layer of pearl oyster shells and freshwater pearl mussel shells are made of nacre. Many other families of mollusks also have an inner shell layer which is nacreous, including marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.

Description

The iridescent nacre inside a Nautilus shell

Nacre is composed of hexagonal platelets of aragonite (calcium carbonate (CaCO₃) crystals) 10-20 µm wide and 0.5 µm thick, arranged in a continuous parallel lamina. These layers are separated by sheets of organic matrix composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins). This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa. Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This design at multiple-length sizes increases its toughness enormously, making it almost equivalent to that of silicon.

Nacre appears iridescent because the thickness of the aragonite platelets is comparable to the wavelength of visible light. This results in constructive and destructive interference of different wavelengths of light, resulting in different colors of light being reflected at different viewing angles.

Nacre is secreted by the epithelial cells of the mantle tissue of some species of mollusk. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging detritus by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called is encystation and it continues as long as the mollusk lives.

Chief sources of mother of pearl are the pearl oyster, found in warm and tropical seas, primarily in Asia; freshwater pearl mussels, which live in many rivers of the United States, Europe, and Asia; and the abalone of California, Japan, other Pacific regions and of the Indian Ocean off Southern Africa. Also widely used for pearl buttons, especially during the 20th century, is the shell of the great green turban snail, Turbo (Lunatica) marmoratus.

Decorative uses

Mother of pearl gunpowder flask from circa 1750, mostly consisting of a polished shell of the large sea snail Turbo marmoratus

Altarpiece, circa 1520, with much carved mother of pearl work

Mother of pearl has been used over many centuries for all kinds of decorative purposes.

Inlay with nacre tesserae
Bagdad pavilion, Topkapı Palace, Istanbul

Interior architectural decoration

Both black and white mother of pearl are used for architectural purposes. The natural mother of pearl may be artificially tinted to almost any color. Mother of pearl tesserae may be cut into shapes and laminated to a ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically 1/16 of an inch thick. The tesserae are then lacquered and polished creating a durable, glossy hard surface.

Instead of using a marble or tile base, the mother of pearl tesserae can be glued to a fiberglass mesh. The result is a lightweight material that offers a seamless installation, and there is no limit to the sheet size. Mother of pearl sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished.

Clothes & accessories

Mother of pearl buttons, also known as "pearl buttons", are used in a decorative or functional way on a variety of clothing such as shirts, sweaters, skirts, jackets and coats.

Pearl buttons as a decoration for clothes are carried to extremes in the costumes of the Pearly Kings and Queens.

Nacre is also used as a decorative feature of watch faces, knives, guns and jewelry.

Musical instruments

Mother of pearl inlay is often used for key touches and various other decorative motifs on musical instruments such as saxophones, bassoons, trumpets, violins, banjos, tamburitzas, guitars and guqins.

Synthetic key touches made of Pyralin or similar imitation nacre materials such as celluloid have been affectionately referred to as mother of toilet seat by musicians. Many accordion and concertina bodies are completely covered in this material.

References

• Lin, A.; Meyers, M.A. (2005-01-15). "Growth and structure in abalone shell". Materials Science and Engineering A 390: 27–41. doi:10.1016/j.msea.2004.06.072. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TXD-4DH2DRS-1&_coverDate=01%2F15%2F2005&_alid=256050522&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=5588&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f4efd0a3d7cf3b4a0b8f9861cff4514d. 
• Mayer, G. (2005). "Rigid biological systems as models for synthetic composites". Science 310: 1144–1147. doi:10.1126/science.1116994. PMID 16293751. 
• Bruet, B.; et al. (September 2005). "Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc Trochus niloticus". J. Mater. Res. 20 (9): 2400. doi:10.1557/JMR.2005.0273. http://web.mit.edu/cortiz/www/Ben/BenPaperRevisedFinal.pdf. 

See also

Wikimedia Commons has media related to: Mother of pearl

Look up nacre in Wiktionary, the free dictionary.

• Ammolite
• Pearl
• Raden