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Removed presumably false statement about nacre formation in sponges. Sponges are not known to create nacre. The research paper abstract states only that it was performed on Unio pictorum, there was probably confusion caused by the research groups study on biomaterials from different organisms, including those created by sponges.
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[[File:Masa perłowa3.jpg|thumb|upright=1.2|Nacreous shell worked into a decorative object]]
[[File:Masa perłowa3.jpg|thumb|upright=1.2|Nacreous shell worked into a decorative object]]


'''Nacre''' ({{IPAc-en|ˈ|n|eɪ|k|ər}} {{respell|NAY|kər}}, {{IPAc-en|also|ˈ|n|æ|k|r|ə}} {{respell|NAK|rə}}),<ref>{{cite Dictionary.com|nacre}}</ref> also known as '''mother of pearl''', is an organic{{ndash}}inorganic [[composite material]] produced by some [[mollusc]]s as an inner [[seashell|shell]] layer; it is also the material of which [[pearl]]s are composed. It is strong, resilient, and [[Iridescence|iridescent]].
'''Nacre''' ({{IPAc-en|ˈ|n|eɪ|k|ər}} {{respell|NAY|kər}}, {{IPAc-en|also|ˈ|n|æ|k|r|ə}} {{respell|NAK|rə}}),<ref>{{cite Dictionary.com|nacre}}</ref> also known as '''mother of pearl''', is an organic{{ndash}}inorganic [[composite material]] produced by some [[mollusc]]s as an inner [[seashell|shell]] layer. It is also the material of which [[pearl]]s are composed. It is strong, resilient, and [[Iridescence|iridescent]].


Nacre is found in some of the most ancient lineages of [[bivalve]]s, [[gastropod]]s, and [[cephalopod]]s. However, the inner layer in the great majority of [[mollusc shell]]s is [[Porcelain|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.
Nacre is found in some of the most ancient lineages of [[bivalve]]s, [[gastropod]]s, and [[cephalopod]]s. However, the inner layer in the great majority of [[mollusc shell]]s is [[Porcelain|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.
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{{biomineralization sidebar|exoskeletons}}
{{biomineralization sidebar|exoskeletons}}


Nacre is composed of hexagonal platelets of [[aragonite]] (a form of [[calcium carbonate]]) 10–20&nbsp;[[µm]] wide and 0.5&nbsp;µm thick arranged in a continuous parallel [[wikt:lamina|lamina]].<ref name="doi10.1016/j.jsb.2005.09.009"/> Depending on the species, the shape of the tablets differs; in ''[[Pinna (bivalve)|Pinna]]'', the tablets are rectangular, with symmetric sectors more or less soluble. Whatever the shape of the tablets, the smallest units they contain are irregular rounded granules.<ref>{{Cite book|title=Biominerals and fossils through time|last=Cuif J.P. Dauphin Y., Sorauf J.E.|date=2011|publisher=Cambridge University Press|isbn=9780521874731|location=Cambridge|oclc=664839176}}</ref> These layers are separated by sheets of organic matrix (interfaces) composed of [[Elasticity (physics)|elastic]] [[biopolymers]] (such as [[chitin]], [[Lustrin A|lustrin]] and [[silk]]-like [[protein]]s). 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&nbsp;[[Pascal (unit)|GPa]] and a yield stress of roughly 70 MPa (when dry).<ref name=Jackson1988 /> Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, spanning multiple length sizes, greatly increases its [[toughness]], making it almost as strong as [[silicon]].<ref name='Gim2019'/>
Nacre is composed of hexagonal platelets of [[aragonite]] (a form of [[calcium carbonate]]) 10–20&nbsp;[[μm]] wide and 0.5&nbsp;μm thick arranged in a continuous parallel [[wikt:lamina|lamina]].<ref name="doi10.1016/j.jsb.2005.09.009"/> Depending on the species, the shape of the tablets differs; in ''[[Pinna (bivalve)|Pinna]]'', the tablets are rectangular, with symmetric sectors more or less soluble. Whatever the shape of the tablets, the smallest units they contain are irregular rounded granules.<ref>{{Cite book|title=Biominerals and fossils through time|last=Cuif J.P. Dauphin Y., Sorauf J.E.|date=2011|publisher=Cambridge University Press|isbn=9780521874731|location=Cambridge|oclc=664839176}}</ref> These layers are separated by sheets of organic matrix (interfaces) composed of [[Elasticity (physics)|elastic]] [[biopolymers]] (such as [[chitin]], [[Lustrin A|lustrin]] and [[silk]]-like [[protein]]s).

⚫
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.<ref name=Abid2018/> However, the negative effects of statistical variations can be offset by interfaces with large strain at failure accompanied by strain hardening.<ref name=Abid2018/> On the other hand, the fracture toughness of nacre increases with moderate statistical variations which creates tough regions where the crack gets pinned.<ref name=Abid2019/> But, higher statistical variations generates very weak regions which allows the crack to propagate without much resistance causing the fracture toughness to decrease.<ref name=Abid2019/> Studies have shown that this weak structural defects act as dissipative topological defects coupled by an elastic distortion.<ref name=Beliaev2021/>


Nacre appears [[Iridescence|iridescent]] because the thickness of the aragonite platelets is close to the wavelength of visible [[light]]. These structures [[interference (wave propagation)|interfere]] constructively and destructively with different wavelengths of light at different viewing angles, creating [[Structural coloration|structural colours]].
Nacre appears [[Iridescence|iridescent]] because the thickness of the aragonite platelets is close to the wavelength of visible [[light]]. These structures [[interference (wave propagation)|interfere]] constructively and destructively with different wavelengths of light at different viewing angles, creating [[Structural coloration|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.<ref name='Metzler2007'/><ref name='Olson2012'/> 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.<ref name=Checa2009/> The interlocking of bricks of nacre has large impact on both the deformation mechanism as well as its toughness.<ref name=r1/> In addition, the mineral–organic interface results in enhanced resilience and strength of the organic interlayers.<ref name=r2/><ref name=r3/><ref name=r4/>
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.<ref name='Metzler2007'/><ref name='Olson2012'/> 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.<ref name=Checa2009/>

=== Mechanical properties ===
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&nbsp;[[Pascal (unit)|GPa]] and a yield stress of roughly 70 MPa (when dry).<ref name="Jackson1988" /> Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, spanning multiple length sizes, greatly increases its [[toughness]], making it almost as strong as [[silicon]].<ref name="Gim2019" /> The mineral–organic interface results in enhanced resilience and strength of the organic interlayers.<ref name="r2" /><ref name="r3" /><ref name="r4" /> The interlocking of bricks of nacre has large impact on both the deformation mechanism as well as its toughness.<ref name="r1" /> [[Tensile testing|Tensile]], [[Shear stress|shear]], and compression tests, [[Weibull distribution|Weibull]] analysis, [[nanoindentation]], and other techniques have all been used to probe the mechanical properties of nacre.<ref name=":0">{{Cite journal |last1=Sun |first1=Jiyu |last2=Bhushan |first2=Bharat |date=2012-08-14 |title=Hierarchical structure and mechanical properties of nacre: a review |journal=RSC Advances |language=en |volume=2 |issue=20 |pages=7617–7632 |doi=10.1039/C2RA20218B |bibcode=2012RSCAd...2.7617S |issn=2046-2069|doi-access=free }}</ref> Theoretical and computational methods have also been developed to explain the experimental observations of nacre's mechanical behavior.<ref>{{Cite journal |last1=Ji |first1=Baohua |last2=Gao |first2=Huajian |date=2004-09-01 |title=Mechanical properties of nanostructure of biological materials |url=https://www.sciencedirect.com/science/article/pii/S0022509604000705 |journal=Journal of the Mechanics and Physics of Solids |language=en |volume=52 |issue=9 |pages=1963–1990 |doi=10.1016/j.jmps.2004.03.006 |bibcode=2004JMPSo..52.1963J |issn=0022-5096}}</ref><ref name=":1">{{Cite journal |last1=Okumura |first1=K. |last2=de Gennes |first2=P.-G. |date=2001-01-01 |title=Why is nacre strong? Elastic theory and fracture mechanics for biocomposites with stratified structures |url=https://doi.org/10.1007/s101890170150 |journal=The European Physical Journal E |language=en |volume=4 |issue=1 |pages=121–127 |doi=10.1007/s101890170150 |bibcode=2001EPJE....4..121O |s2cid=55616061 |issn=1292-8941}}</ref> Nacre is stronger under [[Compressive stress|compressive]] loads than [[tensile]] ones when the force is applied parallel or perpendicular to the platelets.<ref name=":0" /> As an oriented structure, nacre is highly [[Anisotropy|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 [[adhesive force]] needed to separate the proteinaceous and the aragonite phases is high, indicating that there are molecular interactions between the components.<ref name=":0" /> In [[laminated]] structures with hard and soft layers, a model system that can be applied to understand nacre, the [[fracture]] energy and fracture strength are both larger than those values characteristic of the hard material only.<ref name=":1" /> Specifically, this structure facilitates crack deflection, since it is easier for the crack to continue into the [[Viscoelasticity|viscoelastic]] and compliant organic matrix than going straight into another aragonite platelet.<ref name=":0" /><ref name=":2">{{Cite journal |last1=Feng |first1=Q. L. |last2=Cui |first2=F. Z. |last3=Pu |first3=G. |last4=Wang |first4=R. Z. |last5=Li |first5=H. D. |date=2000-06-30 |title=Crystal orientation, toughening mechanisms and a mimic of nacre |url=https://www.sciencedirect.com/science/article/pii/S0928493100001387 |journal=Materials Science and Engineering: C |language=en |volume=11 |issue=1 |pages=19–25 |doi=10.1016/S0928-4931(00)00138-7 |issn=0928-4931|doi-access=free }}</ref> This results in the [[Ductility|ductile]] protein phase deforming such that the crack changes directions and avoids the [[Brittleness|brittle]] ceramic phase.<ref name=":0" /><ref name=":3">{{Cite journal |last1=Grossman |first1=Madeleine |last2=Pivovarov |first2=Dmitriy |last3=Bouville |first3=Florian |last4=Dransfeld |first4=Clemens |last5=Masania |first5=Kunal |last6=Studart |first6=André R. |date=February 2019 |title=Hierarchical Toughening of Nacre‐Like Composites |journal=Advanced Functional Materials |language=en |volume=29 |issue=9 |pages=1806800 |doi=10.1002/adfm.201806800 |s2cid=139307131 |issn=1616-301X|doi-access=free }}</ref> Based on experiments done on nacre-like [[Chemical synthesis|synthetic materials]], it is hypothesized that the compliant matrix needs to have a larger fracture energy than the [[elastic energy]] at fracture of the hard phase.<ref name=":3" /> [[Fiber pull-out]], which occurs in other ceramic [[composite material]]s, contributes to this phenomenon.<ref name=":2" /> Unlike in traditional synthetic composites, the aragonite in nacre forms bridges between individual tablets, so the structure is not only held together by the strong [[adhesion]] of the ceramic phase to the organic one, but also by these connecting [[nanoscale]] features.<ref name=":2" /><ref name=":0" /> As plastic deformation starts, the [[mineral bridge]]s may break, creating small asperities that roughen the aragonite-protein interface.<ref name=":0" /> The additional friction generated by the asperities helps the material withstand shear stresses.<ref name=":0" /> In nacre-like composites, the mineral bridges have also been shown to increase the [[flexural strength]] of the material because they can transfer stress in the material.<ref>{{Cite journal |last1=Magrini |first1=Tommaso |last2=Moser |first2=Simon |last3=Fellner |first3=Madeleine |last4=Lauria |first4=Alessandro |last5=Bouville |first5=Florian |last6=Studart |first6=André R. |date=2020-05-20 |title=Transparent Nacre‐like Composites Toughened through Mineral Bridges |url=http://dx.doi.org/10.1002/adfm.202002149 |journal=Advanced Functional Materials |volume=30 |issue=27 |pages=2002149 |doi=10.1002/adfm.202002149 |s2cid=219464365 |issn=1616-301X|hdl=20.500.11850/417234 |hdl-access=free }}</ref> Developing synthetic composites that exhibit similar mechanical properties as nacre is of interest to scientists working on developing stronger materials. To achieve these effects, researchers take inspiration from nacre and use synthetic ceramics and polymers to mimic 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.<ref name=":0" /> The hardness of this material is also negatively impacted by dehydration.<ref name=":0" /> Water acts as a [[plasticizer]] for the organic matrix, improving its toughness and reducing its shear modulus.<ref name=":0" /> 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.<ref name=":1" />

⚫
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.<ref name="Abid2018" /> However, the negative effects of statistical variations can be offset by interfaces with large strain at failure accompanied by strain hardening.<ref name="Abid2018" /> On the other hand, the [[fracture toughness]] of nacre increases with moderate statistical variations which creates tough regions where the crack gets pinned.<ref name="Abid2019" /> But, higher statistical variations generates very weak regions which allows the crack to propagate without much resistance causing the fracture toughness to decrease.<ref name="Abid2019" /> Studies have shown that this weak structural defects act as dissipative topological defects coupled by an elastic distortion.<ref name="Beliaev2021" />


===Formation===
===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.<ref name='Hovden2015'/> 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.<ref name=Jackson2010/>
Nacre formation is not fully understood. The initial onset assembly, as observed in ''[[Pinna nobilis]]'', is driven by the aggregation of nanoparticles (~50–80 nm) within an organic matrix that arrange in fibre-like polycrystalline configurations.<ref name='Hovden2015'/> The particle number increases successively and, when critical packing is reached, they merge into early-nacre platelets. Nacre growth is mediated by organics, controlling the onset, duration and form of crystal growth.<ref name=Jackson2010/> Individual aragonite "bricks" are believed to quickly grow to the full height of the nacreous layer, and expand until they abut adjacent bricks.<ref name='Checa2009'/> This produces the hexagonal close-packing characteristic of nacre.<ref name='Checa2009'/> Bricks may nucleate on randomly dispersed elements within the organic layer,<ref name=r5/> well-defined arrangements of proteins,<ref name="doi10.1016/j.jsb.2005.09.009"/> or may grow [[epitaxially]] from mineral bridges extending from the underlying tablet.<ref name='Schaffer1997'/><ref name='Checa2011'/> Nacre differs from fibrous aragonite – a brittle mineral of the same form – in that the growth in the c-axis (i.e., approximately perpendicular to the shell, in nacre) is slow in nacre, and fast in fibrous aragonite.<ref name=b1/>


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.<ref name='Checa2009'/> This produces the hexagonal close-packing characteristic of nacre.<ref name='Checa2009'/> The growth of these bricks can be initiated in various ways such as from randomly scattered elements within the organic layer,<ref name=r5/> well-defined arrangements of proteins,<ref name="doi10.1016/j.jsb.2005.09.009"/> or they may expand from mineral bridges coming from the layer underneath.<ref name='Schaffer1997'/><ref name='Checa2011'/>
⚫
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.<ref name=Beliaev2021/><ref>{{cite news |last=Meyers |first=Catherine |date=January 11, 2021 |title=How Mollusks Make Tough, Shimmering Shells |url=https://www.insidescience.org/news/how-mollusks-make-tough-shimmering-shells |work=Inside Science |access-date=June 9, 2021}}</ref>

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.<ref name=b1/>

⚫
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.<ref name=Beliaev2021/><ref>{{cite news |last=Meyers |first=Catherine |date=January 11, 2021 |title=How Mollusks Make Tough, Shimmering Shells |url=https://www.insidescience.org/news/how-mollusks-make-tough-shimmering-shells |work=Inside Science |access-date=June 9, 2021}}</ref>


===Function===
===Function===
[[File:Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone.jpg|thumb|upright=1.2|Fossil [[nautiloid]] shell with original iridescent nacre in fossiliferous asphaltic limestone, [[Oklahoma]]. Dated to the [[Pennsylvanian (geology)|late Middle Pennsylvanian]], which makes it by far the oldest deposit in the world with aragonitic nacreous shelly fossils.<ref>{{Citation|last=John|first=James St|title=Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone (Buckhorn Asphalt, Middle Pennsylvanian; Buckhorn Asphalt Quarry, Oklahoma, USA) 1|date=2007-07-31|url=https://www.flickr.com/photos/jsjgeology/15054496278/|access-date=2023-01-09}}</ref>]]
[[File:Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone.jpg|thumb|upright=1.2|Fossil [[nautiloid]] shell with original iridescent nacre in fossiliferous asphaltic limestone, [[Oklahoma]]. Dated to the [[Pennsylvanian (geology)|late Middle Pennsylvanian]], which makes it by far the oldest deposit in the world with aragonitic nacreous shelly fossils.<ref>{{Cite AV media|last=John|first=James St|title=Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone (Buckhorn Asphalt, Middle Pennsylvanian; Buckhorn Asphalt Quarry, Oklahoma, USA) 1|date=2007-07-31|url=https://www.flickr.com/photos/jsjgeology/15054496278/|access-date=2023-01-09|via=Flickr |type=photo}}</ref>]]
Nacre is secreted by the [[epithelial]] [[cell (biology)|cells]] of the [[Mantle (mollusc)|mantle tissue]] of various molluscs. 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 [[parasite]]s 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.
Nacre is secreted by the [[epithelial]] [[cell (biology)|cells]] of the [[Mantle (mollusc)|mantle tissue]] of various molluscs. 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 [[parasite]]s 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.


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The main commercial sources of mother of pearl have been the [[pearl oyster]], [[freshwater pearl]] mussels, and to a lesser extent the [[abalone]], popular for their sturdiness and beauty in the latter half of the 19th century.
The main commercial sources of mother of pearl have been the [[pearl oyster]], [[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 [[turban snail]] ''[[Turbo marmoratus]]'' and the large top snail, ''[[Tectus niloticus]]''. The international trade in mother of pearl is governed by the [[Convention on International Trade in Endangered Species of Wild Fauna and Flora]], an agreement signed by more than 170 countries.<ref>{{Cite web|date=2010-10-24|title=Contraband Chic: Mother-of-Pearl Items Sell With Export Restrictions &#124; The New York Observer|website=[[The New York Observer]] |url=http://www.observer.com/2010/culture/contraband-chic-mother-pearl-items-sell-export-restrictions|access-date=2023-01-09|archive-url=https://web.archive.org/web/20101024213824/http://www.observer.com/2010/culture/contraband-chic-mother-pearl-items-sell-export-restrictions |archive-date=2010-10-24 }}</ref>
Widely used for pearl buttons especially during the 1900s, were the shells of the great green [[turban snail]] ''[[Turbo marmoratus]]'' and the large top snail, ''[[Tectus niloticus]]''. The international trade in mother of pearl is governed by the [[Convention on International Trade in Endangered Species of Wild Fauna and Flora]], an agreement signed by more than 170 countries.<ref>{{Cite web|author=Jessica Hodin
|date=October 19, 2010|title=Contraband Chic: Mother-of-Pearl Items Sell With Export Restrictions |website=[[The New York Observer]] |url=http://www.observer.com/2010/culture/contraband-chic-mother-pearl-items-sell-export-restrictions|access-date=2023-01-09|archive-url=https://web.archive.org/web/20101024213824/http://www.observer.com/2010/culture/contraband-chic-mother-pearl-items-sell-export-restrictions |archive-date=2010-10-24 }}</ref>


==Uses==
==Uses==
{{sea shell topics}}
{{sea shell topics}}

===Decorative ===
===Decorative ===
====Architecture====
====Architecture====
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====Musical instruments====
====Musical instruments====
Nacre inlay is often used for music [[Key (instrument)|keys]] and other decorative motifs on musical instruments. Many [[accordion]] and [[concertina]] bodies are completely covered in nacre, and some [[guitar]]s have fingerboard or headstock inlays made of nacre (or imitation [[pearloid]] plastic inlays). The [[bouzouki]] and [[baglamas]] (Greek plucked string instruments of the [[lute]] family) typically feature nacre decorations, as does the related Middle Eastern [[oud]] (typically around the [[sound hole]]s and on the back of the instrument). [[bow (music)|Bows]] of stringed instruments such as the [[violin]] and [[cello]] often have mother of pearl inlay at the frog. It is traditionally used on [[saxophone]] keytouches, as well as the valve buttons of [[trumpets]] and other brass instruments. The Middle Eastern [[goblet drum]] (darbuka) is commonly decorated by mother of pearl.{{cn|date=December 2021}}
Nacre inlay is often used for music [[Key (instrument)|keys]] and other decorative motifs on musical instruments. Many [[accordion]] and [[concertina]] bodies are completely covered in nacre, and some [[guitar]]s have fingerboard or headstock inlays made of nacre (or imitation [[pearloid]] plastic inlays). The [[bouzouki]] and [[baglamas]] (Greek plucked string instruments of the [[lute]] family) typically feature nacre decorations, as does the related Middle Eastern [[oud]] (typically around the [[sound hole]]s and on the back of the instrument). [[bow (music)|Bows]] of stringed instruments such as the [[violin]] and [[cello]] often have mother of pearl inlay at the frog. It is traditionally used on [[saxophone]] keytouches, as well as the valve buttons of [[trumpets]] and other brass instruments. The Middle Eastern [[goblet drum]] (darbuka) is commonly decorated by mother of pearl.{{citation needed|date=December 2021}}

====Indian mother of pearl art====
At the end of 19th century, [[Anukul Munsi]] was the first accomplished artist who successfully carved the shells of [[oyster]]s to give a shape of human being which led to the invention of new horizon in Indian contemporary art. For the [[British Empire Exhibition]] in 1924, he received a gold medal.<ref name="Anukul Charan Munshi, the Maverick of Indian Mother-of-Pearl Artistry">{{cite news |title= Anukul Charan Munshi, the Maverick of Indian Mother-of-Pearl Artistry|url=https://webbio257.wixsite.com/anukulcharanmunshith |publisher=Wixsite.com |date=February 5, 2005 |access-date=Sep 22, 2022 |location=Calcutta, India}}</ref><ref name="Anukul Charan Munshi">{{cite news |title= Anukul Charan Munshi|url=https://arthive.com/artists/97278~Anukul_Charan_Munshi |publisher=Arthive |date=February 5, 2005 |access-date=Sep 22, 2022 |location=Calcutta, India}}</ref> His eldest son [[Annada Munsi|Annada Munshi]] is credited with drawing ''Indian Swadesi Movement'' in the form of Indian advertising.<ref>{{Cite web |url=https://www.researchgate.net/figure/Poster-by-Annada-Munshi-for-ITMEB-1947-courtesy-Courtesy-Urban-History-Documentation_fig8_274463295 |title=Poster by Annada Munshi for ITMEB, 1947 |work=Urban History Documentation Archive, Centre for Studies in Social Sciences, Calcutta |via=Researchgate |date= |access-date=24 December 2023}}</ref> Anukul Charan Munshi's third son [[Manu Munsi| Manu Munshi]] was one of the finest mother of pearl artists in the middle of 20th century. As the best example of "Charu and Karu art of Bengal," the former [[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 (Bengal politician)|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.<ref name="Anandabazar Patrika: Munshiana">Anandabazar Patrika. "Munshiana" Publisher: [[Anandabazar Patrika]]</ref><ref name="Artist Manu Munshi">{{cite news |title=Artist Manu Munshi, Renowned Mother of Pearl Artist of India |url=https://srijonmunshi930.wixsite.com/artistmanumunshi |publisher=Wixsite.com |date=February 5, 2005 |access-date=Sep 22, 2022 |location=Calcutta, India}}</ref> His cousin [[Pratip Munsi|Pratip Munshi]] was also a famed mother of pearl artist.<ref name="Santanu Ghosh: Binodane Paikpara Belgachia">{{cite web |author=Santanu Ghosh
|url=https://thecafetable.com/binodane_paikpara_belgachia |title=Binodane Paikpara Belgachia |publisher=Dey's Publishing |date= |access-date=24 December 2023}}</ref><ref name="Santanu Ghosh: Munshianay Chollis Purush">Santanu Ghosh. "Munshianay Chollis Purush" Publisher: Dey's Publishing</ref>


====Other ====
====Other ====
Mother of pearl [[button]]s are used in clothing either for functional or decorative purposes. The [[Pearly Kings and Queens]] are an elaborate example of this.
Mother of pearl [[button]]s 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.{{cn|date=December 2021}}
It is sometimes used in the decorative grips of firearms, and in other gun furniture.{{citation needed|date=December 2021}}


Mother of pearl is sometimes used to make [[spoon]]-like utensils for [[caviar]] (i.e. caviar servers<ref>{{Cite web|title=Ceto the Shrimp - Plate|url=https://www.objetluxe.com/product/ceto-the-shrimp/|access-date=2021-07-14|website=Objet Luxe|language=en-GB}}</ref><ref>{{Cite web|title=Crab Caviar Server|url=https://www.objetluxe.com/product/caviar-server/|access-date=2021-07-14|website=Objet Luxe|language=en-GB}}</ref>) so as to not spoil the taste with metallic spoons.
Mother of pearl is sometimes used to make [[spoon]]-like utensils for [[caviar]] (i.e. caviar servers<ref>{{Cite web|title=Ceto the Shrimp - Plate|url=https://www.objetluxe.com/product/ceto-the-shrimp/|access-date=2021-07-14|website=Objet Luxe|language=en-GB}}</ref><ref>{{Cite web|title=Crab Caviar Server|url=https://www.objetluxe.com/product/caviar-server/|access-date=2021-07-14|website=Objet Luxe|language=en-GB}}{{Dead link|date=June 2024}}</ref>) so as to not spoil the taste with metallic spoons.


<gallery mode="packed" heights="160px" style="float:left">
<gallery mode="packed" heights="160px" style="float:left">
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== Manufactured nacre ==
== Manufactured nacre ==
In 2012, researchers created calcium-based nacre in the laboratory by mimicking its natural growth process.<ref>{{cite journal |doi=10.1038/ncomms1970|pmid=22828626|title=Biomimetic layer-by-layer assembly of artificial nacre|year=2012|last1=Finnemore|first1=Alexander|last2=Cunha|first2=Pedro|last3=Shean|first3=Tamaryn|last4=Vignolini|first4=Silvia|last5=Guldin|first5=Stefan|last6=Oyen|first6=Michelle|last7=Steiner|first7=Ullrich|journal=Nature Communications|volume=3|page=966|bibcode=2012NatCo...3..966F|url=http://discovery.ucl.ac.uk/1446952/1/nacrenatureV8.pdf}}</ref>
In 2012, researchers created calcium-based nacre in the laboratory by mimicking its natural growth process.<ref>{{cite journal |doi=10.1038/ncomms1970|pmid=22828626|title=Biomimetic layer-by-layer assembly of artificial nacre|year=2012|last1=Finnemore|first1=Alexander|last2=Cunha|first2=Pedro|last3=Shean|first3=Tamaryn|last4=Vignolini|first4=Silvia|last5=Guldin|first5=Stefan|last6=Oyen|first6=Michelle|last7=Steiner|first7=Ullrich|journal=Nature Communications|volume=3|page=966|bibcode=2012NatCo...3..966F|s2cid=9004843 |url=http://discovery.ucl.ac.uk/1446952/1/nacrenatureV8.pdf}}</ref>


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.<ref>{{cite web|url=http://www.gizmag.com/mollusk-nacre-tougher-glass/30654 |title=Super-tough glass based on mollusk shells |date=30 January 2014 |publisher=Gizmag.com |access-date=2014-02-13}}</ref>
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.<ref>{{cite web|url=http://www.gizmag.com/mollusk-nacre-tougher-glass/30654 |title=Super-tough glass based on mollusk shells |date=30 January 2014 |publisher=Gizmag.com |access-date=2014-02-13}}</ref>
Line 84: Line 101:
* [[Ammolite]]
* [[Ammolite]]
* [[Pearling in Western Australia]]
* [[Pearling in Western Australia]]
* [[Raden]]
* [[Raden_(Japanese craft)|Raden]]


==References==
==References==
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</ref>
</ref>


<ref name='Checa2009'>{{cite journal|doi = 10.1007/s00114-008-0461-1|title = Nacre and false nacre (foliated aragonite) in extant monoplacophorans (=Tryblidiida: Mollusca)|year = 2008|last1 = Checa|first1 = Antonio G.|last2 = Ramírez-Rico|first2 = Joaquín|last3 = González-Segura|first3 = Alicia|last4 = Sánchez-Navas|first4 = Antonio|journal = Naturwissenschaften|volume = 96|pages = 111–22|pmid = 18843476|issue = 1 |s2cid = 10214928}}</ref>
<ref name='Checa2009'>{{cite journal|doi = 10.1007/s00114-008-0461-1|title = Nacre and false nacre (foliated aragonite) in extant monoplacophorans (=Tryblidiida: Mollusca)|year = 2008|last1 = Checa|first1 = Antonio G.|last2 = Ramírez-Rico|first2 = Joaquín|last3 = González-Segura|first3 = Alicia|last4 = Sánchez-Navas|first4 = Antonio|journal = Naturwissenschaften|volume = 96|pages = 111–22|pmid = 18843476|issue = 1 | bibcode=2009NW.....96..111C |s2cid = 10214928}}</ref>


<ref name="doi10.1016/j.jsb.2005.09.009">{{cite journal|doi=10.1016/j.jsb.2005.09.009|title=Mollusk shell formation: Mapping the distribution of organic matrix components underlying a single aragonitic tablet in nacre|year=2006|last1=Nudelman|first1=Fabio|last2=Gotliv|first2=Bat Ami|last3=Addadi|first3=Lia|last4=Weiner|first4=Steve|journal=Journal of Structural Biology|volume=153|issue=2|pages=176–87|pmid=16413789}}</ref>
<ref name="doi10.1016/j.jsb.2005.09.009">{{cite journal|doi=10.1016/j.jsb.2005.09.009|title=Mollusk shell formation: Mapping the distribution of organic matrix components underlying a single aragonitic tablet in nacre|year=2006|last1=Nudelman|first1=Fabio|last2=Gotliv|first2=Bat Ami|last3=Addadi|first3=Lia|last4=Weiner|first4=Steve|journal=Journal of Structural Biology|volume=153|issue=2|pages=176–87|pmid=16413789}}</ref>


<ref name=r1>{{cite journal|doi=10.1557/JMR.2005.0171|title=Platelet interlocks are the key to toughness and strength in nacre|year=2005|last1=Katti|first1=Kalpana S.|last2=Katti|first2=Dinesh R.|last3=Pradhan|first3=Shashindra M.|last4=Bhosle|first4=Arundhati|journal=Journal of Materials Research|volume=20|issue=5|page=1097|bibcode=2005JMatR..20.1097K}}</ref>
<ref name=r1>{{cite journal|doi=10.1557/JMR.2005.0171|title=Platelet interlocks are the key to toughness and strength in nacre|year=2005|last1=Katti|first1=Kalpana S.|last2=Katti|first2=Dinesh R.|last3=Pradhan|first3=Shashindra M.|last4=Bhosle|first4=Arundhati|journal=Journal of Materials Research|volume=20|issue=5|page=1097|bibcode=2005JMatR..20.1097K|s2cid=135681723 }}</ref>


<ref name=b1>{{cite book|chapter=1.4 |title=Origin of Hard Parts — Early Skeletal Fossils|author = Bruce Runnegar & S Bengtson|chapter-url=http://www.earth-pages.co.uk/Pages%2016-30,%20Section%201.pdf}}</ref>
<ref name=b1>{{cite book|chapter=1.4 |title=Origin of Hard Parts — Early Skeletal Fossils|author = Bruce Runnegar & S Bengtson|chapter-url=http://www.earth-pages.co.uk/Pages%2016-30,%20Section%201.pdf}}</ref>
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<ref name='Checa2011'>{{cite journal|doi=10.1016/j.jsb.2011.09.011|pmid=21982842|title=Mineral bridges in nacre|year=2011|last1=Checa|first1=Antonio|last2=Cartwright|first2=Julyan|author2-link = Julyan Cartwright|last3=Willinger|first3=Marc-Georg|journal=Journal of Structural Biology|volume=176|issue=3|pages=330–339}}</ref>
<ref name='Checa2011'>{{cite journal|doi=10.1016/j.jsb.2011.09.011|pmid=21982842|title=Mineral bridges in nacre|year=2011|last1=Checa|first1=Antonio|last2=Cartwright|first2=Julyan|author2-link = Julyan Cartwright|last3=Willinger|first3=Marc-Georg|journal=Journal of Structural Biology|volume=176|issue=3|pages=330–339}}</ref>


<ref name='Hovden2015'>{{cite journal |doi=10.1038/ncomms10097 |title=Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells|year=2015|last1=Hovden|first1=Robert|last2=Wolf|first2=Stephan|last3=Marin|first3=Frédéric|last4=Holtz|first4=Meganc|last5=Muller|first5=David|last6=Lara|first6=Estroff|journal=Nature Communications|volume=6|pages=10097|pmid=26631940|pmc=4686775|arxiv=1512.02879|bibcode=2015NatCo...610097H}}</ref>
<ref name='Hovden2015'>{{cite journal |doi=10.1038/ncomms10097 |title=Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells|year=2015|last1=Hovden|first1=Robert|last2=Wolf|first2=Stephan|last3=Marin|first3=Frédéric|last4=Holtz|first4=Meganc|last5=Muller|first5=David|last6=Estroff|first6=Lara|journal=Nature Communications|volume=6|pages=10097|pmid=26631940|pmc=4686775|arxiv=1512.02879|bibcode=2015NatCo...610097H}}</ref>


<ref name='Metzler2007'>{{cite journal|doi=10.1103/PhysRevLett.98.268102|title=Architecture of columnar nacre, and implications for its formation mechanism|year=2007|last1=Metzler|first1=Rebecca|last2=Abrecht|first2=Mike|last3=Olabisi|first3=Ronke|last4=Ariosa|first4=Daniel|last5=Johnson|first5=Christopher|last6=Frazer|first6=Bradley|last7=Coppersmith|first7=Susan|author7-link= Susan Coppersmith |last8=Gilbert|first8=PUPA|journal=Physical Review Letters|volume=98|issue=26|pmid=17678131|pages=268102|bibcode=2007PhRvL..98z8102M}}</ref>
<ref name='Metzler2007'>{{cite journal|doi=10.1103/PhysRevLett.98.268102|title=Architecture of columnar nacre, and implications for its formation mechanism|year=2007|last1=Metzler|first1=Rebecca|last2=Abrecht|first2=Mike|last3=Olabisi|first3=Ronke|last4=Ariosa|first4=Daniel|last5=Johnson|first5=Christopher|last6=Frazer|first6=Bradley|last7=Coppersmith|first7=Susan|author7-link= Susan Coppersmith |last8=Gilbert|first8=PUPA|journal=Physical Review Letters|volume=98|issue=26|pmid=17678131|pages=268102|bibcode=2007PhRvL..98z8102M}}</ref>
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| last7 = Ortiz
| last7 = Ortiz
| first7 = C.| bibcode = 2005JMatR..20.2400B
| first7 = C.| bibcode = 2005JMatR..20.2400B
| s2cid = 564507
}}
}}
* Checa, Antonio G.; [[Julyan Cartwright| Julyan H. E. Cartwright]], Marc-Georg Willinger and Steven M. Stanley (Jan. 6, 2009), [https://www.pnas.org/content/106/1/38 "The Key Role of the Surface Membrane in Why Gastropod Nacre Grows in Towers"]; ''Proceedings of the National Academy of Sciences of the United States of America'', Vol. 106, No. 1. {{doi|10.1073/pnas.0808796106}}.
* Checa, Antonio G.; [[Julyan Cartwright|Julyan H. E. Cartwright]], Marc-Georg Willinger and Steven M. Stanley (Jan. 6, 2009), [https://www.pnas.org/content/106/1/38 "The Key Role of the Surface Membrane in Why Gastropod Nacre Grows in Towers"]; ''Proceedings of the National Academy of Sciences of the United States of America'', Vol. 106, No. 1. {{doi|10.1073/pnas.0808796106}}.
* {{cite journal |last1 = Frýda |first1 = J. |last2 = Bandel |first2 = K. |last3 = Frýdová |first3 = B. |year = 2009 | title = Crystallographic texture of Late Triassic gastropod nacre: evidence of long-term stability of the mechanism controlling its formation | journal = [[Bulletin of Geosciences]] | volume = 84 | issue = 4| pages = 745–754 | doi = 10.3140/bull.geosci.1169 | doi-access = free }}
* {{cite journal |last1 = Frýda |first1 = J. |last2 = Bandel |first2 = K. |last3 = Frýdová |first3 = B. |year = 2009 | title = Crystallographic texture of Late Triassic gastropod nacre: evidence of long-term stability of the mechanism controlling its formation | journal = [[Bulletin of Geosciences]] | volume = 84 | issue = 4| pages = 745–754 | doi = 10.3140/bull.geosci.1169 | doi-access = free }}
* {{cite journal
* {{cite journal

Revision as of 16:52, 23 June 2024

"Mother of pearl" redirects here. For other uses, see Mother of pearl (disambiguation).
For the cloud formation, see polar stratospheric cloud.
The iridescent nacre inside a nautilus shell
Nacreous shell worked into a decorative object

Nacre (/ˈneɪkər/ NAY-kər, also /ˈnækrə/ NAK-rə),[1] also known as mother of pearl, is an organic–inorganic composite material produced by some 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 pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.

Physical characteristics

Structure and appearance

Further information: Structural coloration
Schematic of the microscopic structure of nacre layers
Electron microscopy image of a fractured surface of nacre
Part of a series related to
Biomineralization
General
Exoskeletons (shells)
Endoskeletons (bones)
Teeth, scales, tusks etc
Calcification
Silicification
Other forms
Related

Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10–20 μm wide and 0.5 μm thick arranged in a continuous parallel lamina.[2] Depending on the species, the shape of the tablets differs; in Pinna, the tablets are rectangular, with symmetric sectors more or less soluble. Whatever the shape of the tablets, the smallest units they contain are irregular rounded granules.[3] These layers are separated by sheets of organic matrix (interfaces) composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins).

Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures 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 Young's modulus of 70 GPa and a yield stress of roughly 70 MPa (when dry).[7] Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, spanning multiple length sizes, greatly increases its toughness, making it almost as strong as silicon.[8] The mineral–organic interface results in enhanced resilience and strength of the organic interlayers.[9][10][11] The interlocking of bricks of nacre has large impact on both the deformation mechanism as well as its toughness.[12] Tensile, shear, and compression tests, Weibull analysis, nanoindentation, and other techniques have all been used to probe the mechanical properties of nacre.[13] Theoretical and computational methods have also been developed to explain the experimental observations of nacre's mechanical behavior.[14][15] Nacre is stronger under compressive loads than 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 adhesive force needed to separate the proteinaceous and the aragonite phases is high, indicating that there are molecular interactions between the components.[13] In laminated structures with hard and soft layers, a model system that can be applied to understand nacre, the fracture energy and fracture strength are both larger than those values characteristic of the hard material only.[15] Specifically, this structure facilitates crack deflection, since it is easier for the crack to continue into the viscoelastic and compliant organic matrix than going straight into another aragonite platelet.[13][16] This results in the ductile protein phase deforming such that the crack changes directions and avoids the brittle ceramic phase.[13][17] Based on experiments done on nacre-like synthetic materials, it is hypothesized that the compliant matrix needs to have a larger fracture energy than the elastic energy at fracture of the hard phase.[17] Fiber pull-out, which occurs in other ceramic composite materials, contributes to this phenomenon.[16] Unlike in traditional synthetic composites, the aragonite in nacre forms bridges between individual tablets, so the structure is not only held together by the strong adhesion of the ceramic phase to the organic one, but also by these connecting nanoscale features.[16][13] As plastic deformation starts, the mineral bridges may break, creating small asperities that roughen the aragonite-protein interface.[13] The additional friction generated by the asperities helps the material withstand shear stresses.[13] In nacre-like composites, the mineral bridges have also been shown to increase the flexural strength of the material because they can transfer stress in the material.[18] Developing synthetic composites that exhibit similar mechanical properties as nacre is of interest to scientists working on developing stronger materials. To achieve these effects, researchers take inspiration from nacre and use synthetic ceramics and polymers to mimic 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 epithelial cells of the mantle tissue of various molluscs. 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 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

Further information: Mollusc shell § Evolution

The form of nacre varies from group to group. In bivalves, the nacre layer is formed of single crystals in a hexagonal close packing. In gastropods, crystals are twinned, and 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 pearl oyster, 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 turban snail Turbo marmoratus and the large top snail, Tectus niloticus. The international trade in mother of pearl is governed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora, an agreement signed by more than 170 countries.[30]

Uses

Part of a series on
Seashells
Mollusc shells
About mollusc shells
Other seashells

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 keys and other decorative motifs on musical instruments. Many accordion and concertina bodies are completely covered in nacre, and some guitars have fingerboard or headstock inlays made of nacre (or imitation pearloid plastic inlays). The bouzouki and baglamas (Greek plucked string instruments of the lute family) typically feature nacre decorations, as does the related Middle Eastern oud (typically around the sound holes and on the back of the instrument). Bows of stringed instruments such as the violin and cello often have mother of pearl inlay at the frog. It is traditionally used on saxophone keytouches, as well as the valve buttons of 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, Anukul Munsi was the first accomplished artist who successfully carved the shells of oysters to give a shape of human being which led to the invention of new horizon in Indian contemporary art. For the British Empire Exhibition in 1924, he received a gold medal.[31][32] His eldest son Annada Munshi is credited with drawing Indian Swadesi Movement in the form of Indian advertising.[33] Anukul Charan Munshi's third son Manu Munshi was one of the finest mother of pearl artists in the middle of 20th century. As the best example of "Charu and Karu art of Bengal," the former 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

Further information: Pearling in Western Australia

The biotech company Marine Biomedical, formed by a collaboration between the University of Western Australia Medical School and a Broome pearling business, is as of 2021 developing a product nacre to create "PearlBone", which could be used on patients needing bone grafting and reconstructive surgery. The company is applying for regulatory approval in Australia and several other countries, and is expecting it to be approved for clinical use around 2024–5. It is intended to build a factory in the Kimberley region, where pearl shells are plentiful, which would grind the nacre into a product fit for use in biomedical products. Future applications could include dental fillings and 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

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