Editing Chatoyancy

{{Short description|Optical reflectance effect in materials}}
{{Redirect|Cat's eye effect|other uses|Cat's eye (disambiguation){{!}}Cat's eye}}
{{lead|date=October 2023}}
[[File:Tigers-Eye.jpg|thumb|right|[[Tiger's eye]]]]
[[File:Tigers eye crystal444.jpg|thumb|right|Tiger's eye]]

In [[gemology]], '''chatoyancy''' ({{IPAc-en|ʃ|ə|ˈ|t|ɔɪ|.|ən|s|i}} {{respell|shə|TOY|ən|see}}), also called '''chatoyance''' or the '''cat's eye effect''',<ref>{{cite book |first1=Walter|last1=Schumann |first2=Daniel|last2=Reinersmann |translator-first=Elizabeth E.|translator-last=Shea |title=Minerals of the World |year=2008 |publisher=[[Sterling Publishing]] |location=New York |isbn=9781402753398 |page=19 |url=https://books.google.com/books?id=VoCM1wgXLAAC&q=chatoyancy&pg=PA19 |edition=2nd}}</ref> is an [[optical phenomenon|optical]] reflectance effect seen in certain [[gemstone]]s. (Historically, the term has applied specifically to gems; in woods and other materials the effect is more broadly known as "figure" or iridescence.) 

Coined from the French {{lang|fr|œil de chat}}, meaning cat's eye, the chatoyant effect is typically characterized by one or more well-defined bands of reflected light, reminiscent of a cat's eye, which appear to glide across a gem's surface as the object is moved, or when the observer moves while viewing it. 

Chatoyancy is caused by the presence of fibrous structures within the material, such as in [[tiger's eye]] quartz, or by fibrous inclusions and cavities, as seen in cat's eye [[chrysoberyl]], in which the effect is caused by the presence of titanium dioxide, which aligns perpendicularly to produce the effect.<ref>{{cite book|last=Mukherjee|first=Swapna|title=Applied mineralogy : applications in industry and environment|year=2011|publisher=Springer|location=Dordrecht|isbn=978-9400711617|url=https://books.google.com/books?id=mllvP7ZmWqkC&q=chatoyancy&pg=PA381}}</ref><ref>{{cite book|title=The Oxford companion to the earth|year=2006|publisher=Oxford Univ. Press|location=Oxford|isbn=9780198540397|edition=1st|editor-first=Paul L.|editor-last=Hancock|editor-first2=Brian J.|editor-last2=Skinner|chapter=gemstones|url-access=registration|url=https://archive.org/details/oxfordcompaniont00hanc}}</ref>

==Description==
Chatoyancy in the gemstone [[chrysoberyl]] is induced by the presence of the mineral [[rutile]], a mineral primarily composed of [[titanium dioxide]]. These rutile precipitates align perpendicularly, contributing to the cat's eye effect.<ref>{{Citation |title=chrysoberyl |date=2014 |url=http://dx.doi.org/10.1007/978-3-642-41714-6_31903 |work=Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik |pages=224 |access-date=2023-10-20 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg|doi=10.1007/978-3-642-41714-6_31903 |isbn=978-3-642-41713-9 |url-access=subscription }}</ref> This alignment is attributed to the rutile's lattice parameter, which matches only one of the three orthorhombic crystal axes of chrysoberyl, leading to its preferred orientation in that direction. 

===Optimal presentation of effect===
[[File:Cat's Eye super cropped III.jpg|thumb|A [[cabochon]] yellow-green [[quartz]] showing the cat's-eye effect.]]

To bring out the chatoyancy effect, gemstones are typically fashioned into a [[cabochon]] cut, characterized by a rounded, flat base rather than facets, with the fibrous structures aligned parallel to the base. High-quality specimens display a single, sharply defined band of light that moves across the stone when rotated, while lower-quality stones may show a banded effect similar to cat's-eye quartz. Faceted stones do not showcase the effect well.

==== Varieties of chatoyant materials ====
Gem species known for this phenomenon include the aforementioned [[quartz]], [[chrysoberyl]], [[beryl]] (especially. [[Beryl#Aquamarine and maxixe|aquamarine]] varieties), [[charoite]], [[tourmaline]], [[labradorite]], [[Selenite (mineral)|selenite]], [[feldspar]], [[apatite]], [[Moonstone (gemstone)|moonstone]], [[thomsonite]] and [[scapolite]] amongst others. Chatoyancy is not limited to gemstones but can also be found in various wood species and carbon fiber. Synthetically made gemstones with [[Optical fiber|optical fibers]] can also have chatoyancy. These gemstones are available in a variety of vibrant colors.{{citation needed|date=May 2013|reason=Optical fiber gemstones are available but a proper citation is needed.}}

==== Cat's eye terminology ====
[[File:Tigers eye chatometry.gif|thumb|Chatoyance on Tiger's Eye]]
When the term "cat's eye" is used to describe a gemstone by itself, it typically refers to cat's eye chrysoberyl <ref>{{Cite web |title=Cymophane gemstone information |url=https://www.gemdat.org/gem-7481.html |access-date=2023-10-20 |website=www.gemdat.org}}</ref>{{Better source needed|reason=It shows that the stone is also called cat's eye but not that it the only gem called cat's eye|date=October 2023}}. It can also be used as an adjective to indicate the chatoyance phenomenon in another stone, for example, cat's eye [[Aquamarine (gemstone)|aquamarine]].

==In woodworking==
Chatoyancy in wood occurs in various species<ref>{{Cite web |date=2022-05-24 |title=Woodworking word of the day: chatoyance {{!}} Wood |url=https://www.woodmagazine.com/wood-supplies/wood-figure/woodworking-word-of-the-day-chatoyance |access-date=3 August 2022 |website=WOOD Magazine |archive-date=24 May 2022 |archive-url=https://web.archive.org/web/20220524120813/https://www.woodmagazine.com/wood-supplies/wood-figure/woodworking-word-of-the-day-chatoyance |url-status=live }}</ref> – particularly [[hardwood]]s and the various types of [[Nanmu]] woods of China and South East Asia, particularly where stresses from the weight of the growing tree result in denser patches, or where stresses cause [[burl]] or ''[[Bird's eye figure|bird’s eye]]''. This ‘figure’, which has a striking three-dimensional appearance, is highly prized by woodworkers and their clients alike, and is featured regularly in furniture, musical instruments, and other decorative wood products. Figuring takes on a variety of forms and is referred to as ''flame'', ''ribbon'', ''tiger stripe'', ''quilting'', among other names.<ref>{{Cite web |date=2022-01-12 |title=What is Chatoyance? – PZC Chatometry |url=https://www.chatometry.com/what-is-wood-chatoyance/ |access-date=2022-05-24 |website= |archive-url=https://web.archive.org/web/20220112110143/https://www.chatometry.com/what-is-wood-chatoyance/ |archive-date=12 January 2022 |url-status=dead}}</ref>

This effect is sometimes called ''wet look'', since wetting wood with water often displays the chatoyancy, albeit only until the wood dries. Certain finishes cause the [[wood grain]] to become more pronounced. Oil finishes, [[epoxy]], and [[shellac]] can strongly bring out the ''wet look'' effect. When the refractive index of the finish nearly matches that of the wood, light scattering no longer occurs at the wood surface, adding the appearance of depth to the wood's figure.

=== Measurement ===
No method to measure wood chatoyance is unanimously accepted by the scientific community. Some methods have been proposed, such as one named PZC,<ref>{{Cite journal|last1=Pisani|first1=Paolo|last2=Zanetta|first2=Laura|last3=Codoro|first3=Davide|date=2021-12-29|title=Measuring wood chatoyance|url=https://doi.org/10.1080/17480272.2021.2018625|journal=Wood Material Science & Engineering|volume=18 |pages=277–288|doi=10.1080/17480272.2021.2018625|s2cid=245572069|issn=1748-0272|url-access=subscription}}</ref> which was used to measure typical values for a number of wood species; some results are reported below:<ref>{{Cite web|title=PZC Chatometry – A standard system to measure wood chatoyance|url=https://www.chatometry.com/|access-date=2022-01-03|language=it-IT}}</ref>

{| class="wikitable sortable" style="text-align:right;"
!Wood<br>(common name)
!PZC average
|-
|style="text-align:left;"|[[Afrormosia]]
|14.2
|-
|style="text-align:left;"|[[Afzelia]]
|14.1
|-
|style="text-align:left;"|[[Alder]]
|15.0
|-
|style="text-align:left;"|Alder, Red
|16.8
|-
|style="text-align:left;"|[[Anigre]]
|14.4
|-
|style="text-align:left;"|[[Fraxinus|Ash]], American White
|11.5
|-
|style="text-align:left;"|Ash, European
|12.8
|-
|style="text-align:left;"|Ash, Olive
|14.9
|-
|style="text-align:left;"|[[Beech]], European
|10.6
|-
|style="text-align:left;"|[[Birch]]
|18.3
|-
|style="text-align:left;"|[[Black Locust]]
|16.4
|-
|style="text-align:left;"|[[Bocote]]
|11.5
|-
|style="text-align:left;"|[[Bog-wood|Bog Oak]]
|11.6
|-
|style="text-align:left;"|[[Bubinga]]
|19.2
|-
|style="text-align:left;"|[[Cedrus|Cedar]], European
|7.6
|-
|style="text-align:left;"|Cedar, Spanish
|21.3
|-
|style="text-align:left;"|[[Cerejeira]]
|14.1
|-
|style="text-align:left;"|[[Cherry]], Black
|18.0
|-
|style="text-align:left;"|Cherry, Sweet
|15.7
|-
|style="text-align:left;"|[[Chestnut]], Sweet
|14.4
|-
|style="text-align:left;"|[[Cypress]], Mediterranean
|9.3
|-
|style="text-align:left;"|[[Ebony]], Macassar
|11.3
|-
|style="text-align:left;"|[[Elm]]
|14.5
|-
|style="text-align:left;"|[[Etimoe]]
|22.1
|-
|style="text-align:left;"|[[Eucalyptus]]
|13.9
|-
|style="text-align:left;"|[[Fir]], Douglas
|11.1
|-
|style="text-align:left;"|Fir, European Silver
|10.0
|-
|style="text-align:left;"|[[Brya ebenus|Granadillo]]
|14.3
|-
|style="text-align:left;"|[[Guarea]]
|17.2
|-
|style="text-align:left;"|[[Handroanthus|Ipe]]
|11.7
|-
|style="text-align:left;"|[[Iroko]]
|21.8
|-
|style="text-align:left;"|[[Hymenaea courbaril|Jatoba]]
|17.5
|-
|style="text-align:left;"|[[Khaya]]
|23.0
|-
|style="text-align:left;"|[[Koa]]
|26.4
|-
|style="text-align:left;"|[[Pterygota bequaertii|Koto]]
|12.5
|-
|style="text-align:left;"|[[Larch]], European
|10.9
|-
|style="text-align:left;"|[[Terminalia superba|Limba]]
|16.1
|-
|style="text-align:left;"|Limba, Black
|18.7
|-
|style="text-align:left;"|[[Tilia|Lime]], European
|12.2
|-
|style="text-align:left;"|[[Louro Faia]]
|17.4
|-
|style="text-align:left;"|[[Louro Preto]]
|11.3
|-
|style="text-align:left;"|[[Mahogany]], Honduras
|21.4
|-
|style="text-align:left;"|[[Makore]]
|21.0
|-
|style="text-align:left;"|[[Mansonia (plant)|Mansonia]]
|18.0
|-
|style="text-align:left;"|[[Maple]], European
|14.2
|-
|style="text-align:left;"|Maple, Hard
|16.1
|-
|style="text-align:left;"|[[Distemonanthus|Movingui]]
|15.3
|-
|style="text-align:left;"|[[Mulberry]]
|18.2
|-
|style="text-align:left;"|[[Oak]], Red
|12.2
|-
|style="text-align:left;"|Oak, Sessile
|12.6
|-
|style="text-align:left;"|[[Obeche]]
|11.1
|-
|style="text-align:left;"|[[Aucoumea klaineana|Okoume]]
|23.6
|-
|style="text-align:left;"|[[Olive]]
|8.3
|-
|style="text-align:left;"|[[Osage Orange]], Green
|17.0
|-
|style="text-align:left;"|[[Ovangkol]]
|20.0
|-
|style="text-align:left;"|[[Padouk]]
|17.4
|-
|style="text-align:left;"|[[Pear]]
|10.5
|-
|style="text-align:left;"|[[Pine]], Swiss Stone
|10.7
|-
|style="text-align:left;"|Pine, unspecified
|13.2
|-
|style="text-align:left;"|[[Populus|Poplar]]
|14.7
|-
|style="text-align:left;"|Poplar, Yellow
|11.9
|-
|style="text-align:left;"|[[Purpleheart]]
|13.7
|-
|style="text-align:left;"|[[Liquidambar styraciflua|Red Gum]]
|12.6
|-
|style="text-align:left;"|[[Rosewood]], Cocobolo
|9.5
|-
|style="text-align:left;"|Rosewood, Indian
|11.2
|-
|style="text-align:left;"|Rosewood, Kingwood
|14.3
|-
|style="text-align:left;"|Rosewood, Madagascar
|11.7
|-
|style="text-align:left;"|Rosewood, Santos
|12.5
|-
|style="text-align:left;"|[[Sapele]]
|20.7
|-
|style="text-align:left;"|[[Satinwood]]
|13.9
|-
|style="text-align:left;"|[[Spruce]], Fiemme
|9.3
|-
|style="text-align:left;"|[[Sucupira (hardwood)|Sucupira]]
|9.8
|-
|style="text-align:left;"|[[Teak]]
|15.7
|-
|style="text-align:left;"|[[Weinmannia trichosperma|Tineo]]
|14.7
|-
|style="text-align:left;"|[[Juglans|Walnut]], African
|20.2
|-
|style="text-align:left;"|Walnut, Black
|18.6
|-
|style="text-align:left;"|Walnut, European
|17.5
|-
|style="text-align:left;"|[[Wenge]]
|8.5
|-
|style="text-align:left;"|[[Yew]]
|9.8
|-
|style="text-align:left;"|[[Zebrawood]]
|19.1
|-
|style="text-align:left;"|[[Cordia dodecandra|Ziricote]]
|7.0
|}

== See also ==
* {{annotated link|Asterism (gemology)}}
* {{annotated link|Optical phenomena}}

==References==
{{Reflist|30em}}

;General
{{Refbegin}}
* Webster, R., Jobbins, E. A. (Ed.). (1998). ''Gemmologist's compendium.'' St Edmundsbury Press Ltd, Bury St Edwards.
*Mitchell, T. et al. ''Proceedings of the Electron Microscopy Society of America (EMSA)'', 1982.
{{Refend}}

[[Category:Mineralogy]]
[[Category:Optical phenomena]]
[[Category:Wood-related terminology]]