Nacre

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Mother-of-pearl
)
The iridescent nacre inside a nautilus shell
Nacreous shell worked into a decorative object

Nacre (

molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent
.

Nacre is found in some of the most ancient lineages of

bivalves, gastropods, and cephalopods. However, the inner layer in the great majority of mollusc shells is porcellaneous, not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch
pearls.

The outer layer of cultured pearls and the inside layer of

.

Physical characteristics

Structure and appearance

Schematic of the microscopic structure of nacre layers
Electron microscopy image of a fractured surface of nacre

Nacre is composed of hexagonal platelets of

biopolymers (such as chitin, lustrin and silk-like proteins
).

Nacre appears

interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours
.

The crystallographic c-axis points approximately perpendicular to the shell wall, but the direction of the other axes varies between groups. Adjacent tablets have been shown to have dramatically different c-axis orientation, generally randomly oriented within ~20° of vertical.[4][5] In bivalves and cephalopods, the b-axis points in the direction of shell growth, whereas in the monoplacophora it is the a-axis that is this way inclined.[6]

Mechanical properties

This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a

tensile ones when the force is applied parallel or perpendicular to the platelets.[13] As an oriented structure, nacre is highly anisotropic
and as such, its mechanical properties are also dependent on the direction.

A variety of toughening mechanisms are responsible for nacre's mechanical behavior. The

brick-and-mortar
" structure, mineral bridges, and other hierarchical features.

When dehydrated, nacre loses much of its strength and acts as a brittle material, like pure aragonite.[13] The hardness of this material is also negatively impacted by dehydration.[13] Water acts as a plasticizer for the organic matrix, improving its toughness and reducing its shear modulus.[13] Hydrating the protein layer also decreases its Young's modulus, which is expected to improve the fracture energy and strength of a composite with alternating hard and soft layers.[15]

The statistical variation of the platelets has a negative effect on the mechanical performance (stiffness, strength, and energy absorption) because statistical variation precipitates localization of deformation.[19] However, the negative effects of statistical variations can be offset by interfaces with large strain at failure accompanied by strain hardening.[19] On the other hand, the fracture toughness of nacre increases with moderate statistical variations which creates tough regions where the crack gets pinned.[20] But, higher statistical variations generates very weak regions which allows the crack to propagate without much resistance causing the fracture toughness to decrease.[20] Studies have shown that this weak structural defects act as dissipative topological defects coupled by an elastic distortion.[21]

Formation

The process of how nacre is formed is not completely clear. It has been observed in Pinna nobilis, where it starts as tiny particles (~50–80 nm) grouping together inside a natural material. These particles line up in a way that resembles fibers, and they continue to multiply.[22] When there are enough particles, they come together to form early stages of nacre. The growth of nacre is regulated by organic substances that determine how and when the nacre crystals start and develop.[23]

Each crystal, which can be thought of as a "brick", is thought to rapidly grow to match the full height of the layer of nacre. They continue to grow until they meet the surrounding bricks.[6] This produces the hexagonal close-packing characteristic of nacre.[6] The growth of these bricks can be initiated in various ways such as from randomly scattered elements within the organic layer,[24] well-defined arrangements of proteins,[2] or they may expand from mineral bridges coming from the layer underneath.[25][26]

What sets nacre apart from fibrous aragonite, a similarly formed but brittle mineral, is the speed at which it grows in a certain direction (roughly perpendicular to the shell). This growth is slow in nacre, but fast in fibrous aragonite.[27]

A 2021 paper in Nature Physics examined nacre from Unio pictorum, noting that in each case the initial layers of nacre laid down by the organism contained spiral defects. Defects that spiralled in opposite directions created distortions in the material that drew them towards each other as the layers built up until they merged and cancelled each other out. Later layers of nacre were found to be uniform and ordered in structure.[21][28]

Function

Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone, Oklahoma. Dated to the late Middle Pennsylvanian, which makes it by far the oldest deposit in the world with aragonitic nacreous shelly fossils.[29]

Nacre is secreted by the

parasites and damaging debris 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 encystation and it continues as long as the mollusc lives.

In different mollusc groups

The form of nacre varies from group to group. In

cephalopods, they are pseudohexagonal monocrystals, which are often twinned.[6]

Commercial sources

Nacre bracelet

The main commercial sources of mother of pearl have been the

freshwater pearl mussels, and to a lesser extent the abalone
, popular for their sturdiness and beauty in the latter half of the 19th century.

Widely used for pearl buttons especially during the 1900s, were the shells of the great green

Uses

Decorative

Architecture

Both black and white nacre are used for

architectural purposes. The natural nacre may be artificially tinted to almost any color. Nacre 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 about 2 millimetres (0.079 in) thick. The tesserae are then lacquered and polished creating a durable and glossy surface. Instead of using a marble or tile base, the nacre tesserae can be glued to fiberglass. The result is a lightweight material that offers a seamless installation and there is no limit to the sheet size. Nacre 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.[citation needed
]

Musical instruments

Nacre inlay is often used for music

trumpets and other brass instruments. The Middle Eastern goblet drum (darbuka) is commonly decorated by mother of pearl.[citation needed
]

Indian mother of pearl art

At the end of 19th century,

Chief Minister of West Bengal, Dr. Bidhan Chandra Roy, sent Manu's artwork, "Gandhiji's Noakhali Abhiyan", to the United States. Numerous illustrious figures, such as Satyajit Ray, Bidhan Chandra Roy, Barrister Subodh Chandra Roy, Subho Tagore, Humayun Kabir, Jehangir Kabir, as well as his elder brother Annada Munshi, were among the patrons of his works of art. "Indira Gandhi" was one of his famous mother of pearl works of art. He is credited with portraying Tagore in various creative stances that were skillfully carved into metallic plates.[34][35] His cousin Pratip Munshi was also a famed mother of pearl artist.[36][37]

Other

Mother of pearl buttons are used in clothing either for functional or decorative purposes. The Pearly Kings and Queens are an elaborate example of this.

It is sometimes used in the decorative grips of firearms, and in other gun furniture.[citation needed]

Mother of pearl is sometimes used to make spoon-like utensils for caviar (i.e. caviar servers[38][39]) so as to not spoil the taste with metallic spoons.

Biomedical use

The biotech company Marine Biomedical, formed by a collaboration between the

spinal surgery.[40]

Manufactured nacre

In 2012, researchers created calcium-based nacre in the laboratory by mimicking its natural growth process.[41]

In 2014, researchers used lasers to create an analogue of nacre by engraving networks of wavy 3D "micro-cracks" in glass. When the slides were subjected to an impact, the micro-cracks absorbed and dispersed the energy, keeping the glass from shattering. Altogether, treated glass was reportedly 200 times tougher than untreated glass.[42]

See also

References

  1. ^ "nacre". Dictionary.com Unabridged (Online). n.d.
  2. ^
    PMID 16413789
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  4. .
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  6. ^ .
  7. ^ Jackson, A. P.; Vincent, J. F. V; Turner, R. M. (1988). "The mechanical design of nacre". Proceedings of the Royal Society B: Biological Sciences. 234 (1277) (published 22 Sep 1988): 415–440.
    S2CID 135544277
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  16. ^ .
  17. ^ .
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  19. ^ a b Abid, N.; Mirkhalaf, M.; Barthelat, F. (2018). "Discrete-element modeling of nacre-like materials: effects of random microstructures on strain localization and mechanical performance". Journal of the Mechanics and Physics of Solids. 112: 385–402. .
  20. ^ a b Abid, N.; Pro, J. W.; Barthelat, F. (2019). "Fracture mechanics of nacre-like materials using discrete-element models: Effects of microstructure, interfaces and randomness". Journal of the Mechanics and Physics of Solids. 124: 350–365.
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  21. ^ a b Beliaev, N.; Zöllner, D.; Pacureanu, A.; Zaslansky, P.; Zlotnikov, I. (2021). "Dynamics of topological defects and structural synchronization in a forming periodic tissue". Nature Physics. 124 (3): 350–365.
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  27. ^ Bruce Runnegar & S Bengtson. "1.4" (PDF). Origin of Hard Parts — Early Skeletal Fossils.
  28. ^ Meyers, Catherine (January 11, 2021). "How Mollusks Make Tough, Shimmering Shells". Inside Science. Retrieved June 9, 2021.
  29. ^ John, James St (2007-07-31). Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone (Buckhorn Asphalt, Middle Pennsylvanian; Buckhorn Asphalt Quarry, Oklahoma, USA) 1 (photo). Retrieved 2023-01-09 – via Flickr.
  30. ^ Jessica Hodin (October 19, 2010). "Contraband Chic: Mother-of-Pearl Items Sell With Export Restrictions". The New York Observer. Archived from the original on 2010-10-24. Retrieved 2023-01-09.
  31. ^ "Anukul Charan Munshi, the Maverick of Indian Mother-of-Pearl Artistry". Calcutta, India: Wixsite.com. February 5, 2005. Retrieved Sep 22, 2022.
  32. ^ "Anukul Charan Munshi". Calcutta, India: Arthive. February 5, 2005. Retrieved Sep 22, 2022.
  33. ^ "Poster by Annada Munshi for ITMEB, 1947". Urban History Documentation Archive, Centre for Studies in Social Sciences, Calcutta. Retrieved 24 December 2023 – via Researchgate.
  34. ^ Anandabazar Patrika. "Munshiana" Publisher: Anandabazar Patrika
  35. ^ "Artist Manu Munshi, Renowned Mother of Pearl Artist of India". Calcutta, India: Wixsite.com. February 5, 2005. Retrieved Sep 22, 2022.
  36. ^ Santanu Ghosh. "Binodane Paikpara Belgachia". Dey's Publishing. Retrieved 24 December 2023.
  37. ^ Santanu Ghosh. "Munshianay Chollis Purush" Publisher: Dey's Publishing
  38. ^ "Ceto the Shrimp - Plate". Objet Luxe. Retrieved 2021-07-14.
  39. ^ "Crab Caviar Server". Objet Luxe. Retrieved 2021-07-14.
  40. ^ Fowler, Courtney (28 October 2021). "Kimberley mother-of-pearl could become synthetic bone in world-first medical collaboration". ABC News. Australian Broadcasting Corporation. Retrieved 29 December 2021.
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  42. ^ "Super-tough glass based on mollusk shells". Gizmag.com. 30 January 2014. Retrieved 2014-02-13.

Further reading

External links