Editing Ruby

{{short description|Variety of corundum, mineral, gemstone}}
{{about|the gemstone|the programming language|Ruby (programming language)|people with the given name|Ruby (name)|annotations above East Asian characters|Ruby character|other uses|Ruby (disambiguation)}}
{{Use American English|date=August 2015}}
{{Use dmy dates|date=March 2024}}
{{Infobox mineral
|boxbgcolor        = #b31b1d
|boxtextcolor      = #ffffff
| name             = Ruby
| image            = File:Corundum-215330.jpg
| imagesize        = 260px
| alt              =
| caption          = A ruby crystal from [[Dodoma Region]], [[Tanzania]]
| category         = [[Oxide minerals|Oxide]] [[minerals]], [[corundum]] [[Mineral variety|variety]]
| formula          = [[aluminium oxide]] with [[chromium]], Al{{sub|2}}O{{sub|3}}:Cr
| molweight        =
| strunz           =
| dana             =
| system           = [[Trigonal]] 
| class            = Hexagonal scalenohedral ({{overline|3}}m) <br/>[[H-M symbol]]: ({{overline|3}}2/m)
| symmetry         = ''R''{{overline|3}}c<ref>[http://webmineral.com/data/Corundum.shtml Corundum data on Webmineral] {{webarchive |url=https://web.archive.org/web/20071001144657/http://webmineral.com/data/Corundum.shtml |date=1 October 2007}}</ref>
| unit cell        =
| color            = Orangy red through strongly purplish red.
| habit            = Terminated tabular hexagonal prisms
| twinning         =
| cleavage         = No true cleavage
| fracture         = Conchoidal, splintery
| tenacity         = Brittle
| mohs             = 9.0
| luster           = Subadamantine, vitreous, pearly (on partings)
| streak           = White
| diaphaneity      = Transparent, translucent
| gravity          = 3.97–4.05
| density          =
| polish           =
| opticalprop      = Uniaxial/−
| refractive       = n{{sub|ω}}=1.768–1.772 <br/>n{{sub|ε}}=1.760–1.763
| birefringence    = 0.008 to 0.010
| pleochroism      = Strong: purplish-red – orangy-red
| 2V               =
| dispersion       = 0.018
| extinction       =
| length fast/slow =
| fluorescence     = Red under longwave
| absorption       =
| melt             = 
| fusibility       =
| diagnostic       =
| solubility       = 
| impurities       = Cr. (sometimes: Ti, Fe)
| alteration       =
| other            =
| prop1            =
| prop1text        =
| references       =<ref>[https://www.gemdat.org/gem-3473.html Ruby on Gemdat.org] {{webarchive |url=https://web.archive.org/web/20210903162228/https://www.gemdat.org/gem-3473.html |date=3 September 2021}}</ref>
}}
[[File:Rubis gisements.jpg|thumb|upright=1.25|The main ruby-producing countries]]

'''Ruby''' is a [[pink]]ish-red-to-blood-red-colored [[gemstone]], a variety of the [[mineral]] [[corundum]] ([[aluminium oxide]]). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called [[sapphire]]s; given that the rest of the corundum species are called as such, rubies are sometimes referred to as "red sapphires".

Ruby is one of the traditional [[cardinal gem]]s, alongside [[amethyst]], [[sapphire]], [[emerald]], and [[diamond]].<ref>[https://books.google.com/books?id=crc7ZtRHItgC&pg=PA1 ''Precious Stones''] {{webarchive |url=https://web.archive.org/web/20171218182752/https://books.google.com/books?id=crc7ZtRHItgC&pg=PA1 |access-date=18 December 2017}}, Max Bauer, p. 2</ref> The word ''ruby'' comes from ''ruber'', [[Latin]] for red. The color of a ruby is due to the presence of [[chromium]].

Some gemstones that are popularly or historically called rubies, such as the [[Black Prince's Ruby]] in the British [[Imperial State Crown]], are actually [[spinel]]s. These were once known as "Balas rubies".

The quality of a ruby is determined by its color, cut, and clarity, which, along with [[Carat (mass)|carat]] weight, affect its value. The brightest and most valuable shade of red, called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. After color comes clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like [[rutile]] [[Inclusion (mineral)|inclusions]] may indicate that the stone has been treated. Ruby is the traditional [[birthstone]] for July and is usually pinker than [[garnet]], although some [[rhodolite]] garnets have a similar pinkish hue to most rubies. The world's most valuable ruby to be sold at auction is the [[Estrela de Fura]], which sold for US$34.8 million.<ref>{{Cite web |last=Holland |first=Oscar |date=8 June 2023 |title=Largest ruby ever to come to auction sells for record-breaking $34.8 million |url=https://www.cnn.com/style/ruby-sothebys-auction-record/index.html |access-date=22 September 2023 |website=CNN |language=en |archive-date=22 September 2023 |archive-url=https://web.archive.org/web/20230922031042/https://www.cnn.com/style/ruby-sothebys-auction-record/index.html |url-status=live }}</ref>

==Physical properties==
[[Image:Corundum.png|thumb|Crystal structure of rubies]]
Rubies have a [[hardness]] of 9.0 on the [[Mohs scale of mineral hardness]]. Among the natural gems, only [[moissanite]] and [[diamond]] are harder, with diamond having a Mohs hardness of 10.0 and moissanite falling somewhere in between corundum (ruby) and diamond in hardness. Sapphire, ruby, and pure corundum are α-alumina, the most stable form of Al{{sub|2}}O{{sub|3}}, in which 3 electrons leave each aluminium [[ion]] to join the regular octahedral group of six nearby O{{sup|2−}} ions; in pure corundum this leaves all of the aluminium ions with a very stable configuration of no unpaired electrons or unfilled energy levels, and the crystal is perfectly colorless, and transparent except for flaws.

[[Image: Ruby model.jpg|thumb|Crystal structure of ruby showing the substitution of Al{{sup|3+}} ions (blue) with Cr{{sup|3+}} (red).  The substitution density of Cr{{sup|3+}} ions in this model is approximately 2%, approximating the maximum doping normally encountered.<ref>{{cite web| url = https://www.miramodus.com/images.shtml| title = Images of molecular models from Miramodus| access-date = 28 June 2019| archive-date = 24 November 2018| archive-url = https://web.archive.org/web/20181124162526/https://www.miramodus.com/images.shtml| url-status = live}}</ref>]]

When a chromium atom replaces an occasional aluminium atom, it too loses 3 electrons to become a chromium{{sup|3+}} ion to maintain the charge balance of the Al{{sub|2}}O{{sub|3}} crystal.  However, the Cr{{sup|3+}} ions are larger and have [[Electron configuration#Ionization of the transition metals|electron orbitals]] in different directions than aluminium. The octahedral arrangement of the O{{sup|2−}} ions is distorted, and the energy levels of the different orbitals of those Cr{{sup|3+}} ions are slightly altered because of the directions to the O{{sup|2−}} ions.<ref name=causes>{{cite web | url= http://www.webexhibits.org/causesofcolor/6AA.html | title= Ruby: causes of color | access-date= 28 March 2016 | url-status= live | archive-url= https://web.archive.org/web/20160321193313/http://www.webexhibits.org/causesofcolor/6AA.html | archive-date= 21 March 2016 | df= mdy-all }}</ref> Those energy differences correspond to absorption in the ultraviolet, violet, and yellow-green regions of the spectrum.

[[Image:Ruby transmittance.svg |thumb|Transmittance of ruby in optical and near-IR spectra. Note the two broad violet and yellow-green absorption bands and one narrow absorption band at the wavelength of 694 nm, which is the wavelength of the ruby laser.]]

If one percent of the aluminium ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem.<ref name=causes/>  Additionally, absorption at any of the above wavelengths stimulates [[fluorescence|fluorescent]] emission of 694-nanometer-wavelength red light, which adds to its red color and perceived [[Lustre (mineralogy)|luster]].<ref>{{Cite web|title=Ruby Crystal Fluorescence|url=https://physicsopenlab.org/2020/06/15/ruby-crystal-fluorescence/|access-date=4 May 2021|website=PhysicsOpenLab|language=en-US|archive-date=4 May 2021|archive-url=https://web.archive.org/web/20210504014108/https://physicsopenlab.org/2020/06/15/ruby-crystal-fluorescence/|url-status=live}}</ref> The chromium concentration in artificial rubies can be adjusted during the crystal growth process to be ten to twenty times lower than in natural gemstones. [[Theodore Maiman]] says that "because of the low chromium level in these crystals they display a lighter red color than gemstone ruby and are referred to as '''pink ruby'''."<ref name="maiman18">{{cite book |doi=10.1007/978-3-319-61940-8|title=The Laser Inventor|series=Springer Biographies|year=2018|isbn=978-3-319-61939-2}}</ref>

After absorbing short-wavelength light, there is a short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs. If 694-nanometer photons pass through the crystal during that time, they can stimulate more fluorescent photons to be emitted in-phase with them, thus strengthening the intensity of that red light. By arranging mirrors or other means to pass  emitted light repeatedly through the crystal, a [[ruby laser]] in this way produces a very high intensity of [[Coherence (physics)|coherent]] red light.

All natural rubies have imperfections in them, including color impurities and inclusions of [[rutile]] needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. Usually, the rough stone is heated before cutting. These days, almost all rubies are treated in some form, with heat treatment being the most common practice. Untreated rubies of high quality command a large premium.

Some rubies show a three-point or six-point [[asterism (gemmology)|asterism]] or "star". These rubies are cut into [[cabochons]] to display the effect properly. Asterisms are best visible with a single-light source and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the "silk" (the structurally oriented [[rutile]] needle inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show color changes—though this occurs very rarely—as well as [[chatoyancy]] or the "cat's eye" effect.

===Versus pink sapphire===
Generally, gemstone-quality corundum in all shades of red, including pink, are called rubies.<ref name="matlins">{{cite book|last=Matlins|first=Antoinette Leonard|title=Colored Gemstones|year=2010|publisher=Gemstone Press|isbn=978-0-943763-72-9|page=203|url=https://books.google.com/books?id=4UANp6MCTSQC|url-status=live|archive-url=https://web.archive.org/web/20160502140108/https://books.google.com/books?id=4UANp6MCTSQC|archive-date=2 May 2016}}</ref><ref>{{cite book|last=Reed|first=Peter|title=Gemmology|year=1991|publisher=Butterworth-Heinemann|isbn=0-7506-6449-5|page=337|url=https://books.google.com/books?id=t-OQO3Wk-JsC|url-status=live|archive-url=https://web.archive.org/web/20170102012607/https://books.google.com/books?id=t-OQO3Wk-JsC|archive-date=2 January 2017}}</ref>  However, in the United States, a minimum color saturation must be met to be called a ruby; otherwise, the stone will be called a [[sapphire|pink sapphire]].<ref name="matlins" />  Drawing a distinction between rubies and pink sapphires is relatively new, having arisen sometime in the 20th century. Often, the distinction between ruby and pink sapphire is not clear and can be debated. As a result of the difficulty and subjectiveness of such distinctions, trade organizations such as the International Colored Gemstone Association (ICGA) have adopted the broader definition for ruby which encompasses its lighter shades, including pink.

==Occurrence and mining==
Historically, rubies have been mined in [[Thailand]], in the [[Pailin]] and [[Samlout District]] of [[Cambodia]], as well as in [[Afghanistan]], [[Australia]], [[Brazil]], [[Colombia]], [[India]], [[Namibia]], [[Japan]], and Scotland. After the [[Second World War]], ruby deposits were found in [[Madagascar]], [[Mozambique]], Nepal, Pakistan, [[Tajikistan]], [[Tanzania]], and [[Vietnam]].<ref>{{cite web |url=http://www.gemsociety.org/article/ruby-sapphire-identifying-origin-understanding-value-rarity-gem-corundum/ |title=Ruby and Sapphire Origins |access-date=23 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20141230213525/http://www.gemsociety.org/article/ruby-sapphire-identifying-origin-understanding-value-rarity-gem-corundum/ |archive-date=30 December 2014  }}</ref>

The [[Republic of North Macedonia]] is the only country in mainland Europe to have naturally occurring rubies. They can mainly be found around the city of [[Prilep]]. Macedonian rubies have a unique raspberry color.<ref>{{Cite web |last=Caucaso |first=Osservatorio Balcani e |title=A Macedonian Ruby |url=https://www.balcanicaucaso.org/eng/Areas/North-Macedonia/A-Macedonian-Ruby-141923 |access-date=21 March 2024 |website=OBC Transeuropa |language=it |archive-date=21 March 2024 |archive-url=https://web.archive.org/web/20240321214140/https://www.balcanicaucaso.org/eng/Areas/North-Macedonia/A-Macedonian-Ruby-141923 |url-status=live }}</ref>

A few rubies have been found in the U.S. states of [[Montana]], [[North Carolina]], [[South Carolina]] and [[Wyoming]].<ref>{{Cite journal |last1=Giuliani |first1=Gaston |last2=Groat |first2=Lee A. |last3=Fallick |first3=Anthony E. |last4=Pignatelli |first4=Isabella |last5=Pardieu |first5=Vincent |date=July 2020 |title=Ruby Deposits: A Review and Geological Classification |journal=Minerals |language=en |volume=10 |issue=7 |pages=597 |doi=10.3390/min10070597 |doi-access=free |bibcode=2020Mine...10..597G |issn=2075-163X}}</ref>

[[Spinel]], another red gemstone, is sometimes found along with rubies in the same gem gravel or marble. Red spinels may be mistaken for rubies by those lacking experience with gems. However, the finest red spinels, now heavily sought, can have values approaching all but the finest examples of ruby.<ref>{{Cite book|author1=Wenk, Hans-Rudolf |author2=Bulakh, A. G. |title=Minerals: their constitution and origin|year=2004 |publisher=Cambridge University Press|location=Cambridge, U.K. |isbn=0-521-52958-1 |pages=539–541 |url=https://books.google.com/books?id=0GAvKQJ2JuwC&pg=RA1-PA541}}</ref><ref>{{cite news |author=Kathleen Beckett |title=Spinel: 'The Great Impostor' No More |work=The New York Times |date=10 February 2020 |url=https://www.nytimes.com/2020/02/10/fashion/jewelry-spinel-christies-sothebys-cartier.html |access-date=1 January 2023 |archive-date=29 December 2022 |archive-url=https://web.archive.org/web/20221229073415/https://www.nytimes.com/2020/02/10/fashion/jewelry-spinel-christies-sothebys-cartier.html |url-status=live }}</ref>
The [[Mogok]] Valley in [[Upper Myanmar]] (Burma) was for centuries the world's main source for rubies. That region has produced some exceptional rubies; however, in recent years few good rubies have been found. In central Myanmar, the area of Mong Hsu began producing rubies during the 1990s and rapidly became the world's main ruby mining area. The most recently found ruby deposit in Myanmar is in Namya (Namyazeik) located in the northern state of [[Kachin State|Kachin]].<ref>{{cite news |title=Burmese Ruby – The King of Natural Ruby Gem Stone |url=https://www.starlanka.com/journal/burma-ruby-the-king-of-natural-ruby-gem-stone/ |access-date=25 March 2022 |archive-date=25 March 2022 |archive-url=https://web.archive.org/web/20220325103720/https://www.starlanka.com/journal/burma-ruby-the-king-of-natural-ruby-gem-stone/ |url-status=live }}</ref>

In [[Azad Kashmir|Pakistani Kashmir]] there are vast proven reserves of millions of rubies, worth up to half a billion dollars.<ref>{{cite news|title=Rubies, the buried treasures of Pakistani Kashmir|url=https://www.france24.com/en/20171015-rubies-buried-treasures-pakistani-kashmir|publisher=[[France24]]|access-date=22 June 2019|archive-date=22 June 2019|archive-url=https://web.archive.org/web/20190622184601/https://www.france24.com/en/20171015-rubies-buried-treasures-pakistani-kashmir|url-status=live}}</ref> However, as of 2017 there was only one mine (at Chitta Katha) due to lack of investment.<ref>{{cite news|author=Caroline Nelly Perrot|title=Rubies, the buried treasures of Pakistani Kashmir|url=https://phys.org/news/2017-10-rubies-treasures-pakistani-kashmir.html|access-date=22 June 2019|archive-date=22 June 2019|archive-url=https://web.archive.org/web/20190622184602/https://phys.org/news/2017-10-rubies-treasures-pakistani-kashmir.html|url-status=live}}</ref> In [[Afghanistan]], rubies are mined at Jegdalek.<ref>{{cite magazine|title=The dangerous world of Pakistan's gem trade|url=https://www.macleans.ca/news/world/pakistans-blood-stones/|magazine=[[Maclean's]]|access-date=22 June 2019|archive-date=22 June 2019|archive-url=https://web.archive.org/web/20190622184601/https://www.macleans.ca/news/world/pakistans-blood-stones/|url-status=live}}</ref> In 2017 the Aappaluttoq mine in Greenland began running.<ref>{{Cite web|title=GIA – Greenland Ruby|url=https://www.gia.edu/gems-gemology/spring-2019-gemnews-greenland-ruby-update|website=www.gia.edu|access-date=25 March 2022|archive-date=19 May 2022|archive-url=https://web.archive.org/web/20220519183925/https://www.gia.edu/gems-gemology/spring-2019-gemnews-greenland-ruby-update|url-status=live}}</ref>

The rubies in Greenland are said to be among the oldest in the world at approximately 3 billion years old. The Aappaluttoq mine in Greenland is located 160 kilometers south of Nuuk, the capital of Greenland. The rubies are traceable from mine to market.<ref>{{Cite journal |last=Vertriest |first=Wim |date=Spring 2019 |title=Greenland Ruby Update |url=https://www.gia.edu/gems-gemology/spring-2019-gemnews-greenland-ruby-update |journal=Gems & Gemology |volume=55 |issue=1}}</ref>

The Montepuez ruby mine in northeastern Mozambique is situated on one of the most significant ruby deposits in the world,<ref>{{Cite web|title=Mozambique: A Ruby Discovery for the 21st Century {{!}} Gems & Gemology|url=http://www.gia.edu/sites/Satellite?c=Page&cid=1495237981372&childpagename=GIA/Page/GGArticleDetail&pagename=GIA/Wrapper&WRAPPERPAGE=GIA/Wrapper|access-date=10 December 2021|website=www.gia.edu|language=en|archive-date=9 December 2021|archive-url=https://web.archive.org/web/20211209163204/https://www.gia.edu/sites/Satellite?c=Page&cid=1495237981372&childpagename=GIA/Page/GGArticleDetail&pagename=GIA/Wrapper&WRAPPERPAGE=GIA/Wrapper|url-status=live}}</ref> although, rubies were only discovered here for the first time in 2009. In less than a decade, Mozambique has become the world's most productive source for gem-quality ruby.<ref>{{Cite journal |last=Wim |first=Vertriest |date=Summer 2019 |title=RUBY FROM MOZAMBIQUE: A REVIEW |url=https://www.gia.edu/doc/GG-SU19-Vertriest.pdf |journal=Gems and Gemology}}</ref><ref>{{Cite news |last=Lankarani |first=Nazanin |date=2023-07-02 |title=When It Comes to Rubies, Is Mozambique the New Star? |url=https://www.nytimes.com/2023/07/02/fashion/jewelry-rubies-mozambique.html |access-date=2024-06-27 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>

==Factors affecting value==
{{Unreferenced section|date=May 2022}}
Rubies, as with other gemstones, are graded using criteria known as the four Cs, namely color, cut, clarity and carat weight. Rubies are also evaluated on the basis of their geographic origin.

=== Color ===
[[File:Rubin (Corundum) - Hunza Valley, div. Gilgit, Northern Areas, Pakistan.jpg|thumb|Ruby (Corundum) - Hunza Valley, div. Gilgit, Northern Areas, Pakistan.]]
In the evaluation of colored gemstones, color is the most important factor. Color divides into three components: ''hue'', ''saturation'' and ''tone''. Hue refers to color as we normally use the term. Transparent gemstones occur in the ''pure spectral hues'' of red, orange, yellow, green, blue, violet.<ref name="wise">{{cite book|author=Wise, Richard W. |title=Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones |pages=18–22 |isbn=0-9728223-8-0 |year=2006|publisher=Brunswick House Press}}</ref> In nature, there are rarely pure hues, so when speaking of the hue of a gemstone, we speak of primary and secondary and sometimes tertiary hues. Ruby is defined to be red. All other hues of the gem species corundum are called sapphire. Ruby may exhibit a range of secondary hues, including orange, purple, violet, and pink.

<gallery mode="packed" heights="160">
Image:Ruby cristal.jpg|A naturally occurring ruby crystal
Image:Ruby gem.JPG|Natural ruby with inclusions
Image:Cut Ruby.jpg|A cut pink ruby
Image:Rubis, calcite 14.jpg|Purple rubies
</gallery>

=== Clarity ===
Because rubies host many inclusions, their clarity is evaluated by the inclusions’ size, number, location, and visibility. Rubies with the highest clarity grades are known as “eye-clean,” because their inclusions are the least visible to the naked human eye.<ref>{{Cite web|title=Ruby and Sapphire Grading Tools|url=https://www.gemsociety.org/article/ruby-sapphire-grading-tools/|access-date=4 May 2021|website=International Gem Society|language=en|archive-date=4 May 2021|archive-url=https://web.archive.org/web/20210504012848/https://www.gemsociety.org/article/ruby-sapphire-grading-tools/|url-status=live}}</ref> Rubies may also have thin, intersecting inclusions called silk. Silk can scatter light, brightening the gem's appearance, and the presence of silk can also show whether a ruby has been previously heat treated, since intense heat will degrade a ruby's silk.

==Treatments and enhancements==
Improving the quality of gemstones by treating them is common practice. Some treatments are used in almost all cases and are therefore considered acceptable. During the late 1990s, a large supply of low-cost materials caused a sudden surge in supply of heat-treated rubies, leading to a downward pressure on ruby prices.

Improvements used include color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them.

The most common treatment is the application of heat. Most rubies at the lower end of the market are heat treated to improve color, remove ''purple tinge'', blue patches, and silk. These heat treatments typically occur around temperatures of 1800&nbsp;°C (3300&nbsp;°F).<ref name="ThemelisRubyHeat">{{cite book|isbn=0940965100|title=The Heat Treatment of Ruby and Sapphire|publisher=Gemlab Inc.|place=Bangkok, Thailand|year=1992}}</ref> Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300&nbsp;°C (2400&nbsp;°F) for 20 to 30 minutes. The silk is partially broken, and the color is improved.

Another treatment, which has become more frequent in recent years, is <!-- to avoid false positives for 'is led/lead' typo-->[[lead glass]] filling. Filling the fractures inside the ruby with lead glass (or a similar material) dramatically improves the transparency of the stone, making previously unsuitable rubies fit for applications in jewelry.<ref>Vincent Pardieu [http://www.fieldgemology.org/Ruby_lead_glass_treatment.pdf Lead Glass Filled/Repaired Rubies] {{webarchive|url=https://web.archive.org/web/20110831062843/http://www.fieldgemology.org/Ruby_lead_glass_treatment.pdf |date=31 August 2011 }}. Asian Institute of Gemological Sciences Gem Testing Laboratory. February 2005</ref> The process is done in four steps:

# The rough stones are pre-polished to eradicate all surface impurities that may affect the process
# The rough is cleaned with [[hydrogen fluoride]]
# The first heating process during which no fillers are added. The heating process eradicates impurities inside the fractures. Although this can be done at temperatures up to 1400&nbsp;°C (2500&nbsp;°F) it most likely occurs at a temperature of around 900&nbsp;°C (1600&nbsp;°F) since the rutile silk is still intact.
# The second heating process in an electrical oven with different chemical additives. Different solutions and mixes have shown to be successful; however, mostly lead-containing glass-powder is used at present. The ruby is dipped into oils, then covered with powder, embedded on a tile and placed in the oven where it is heated at around 900&nbsp;°C (1600&nbsp;°F) for one hour in an oxidizing atmosphere. The orange colored powder transforms upon heating into a transparent to yellow-colored paste, which fills all fractures. After cooling the color of the paste is fully transparent and dramatically improves the overall transparency of the ruby.<ref>Richard W. Hughes (1997), ''Ruby & Sapphire'', Boulder, CO, RWH Publishing, {{ISBN|978-0-9645097-6-4}}</ref>

If a color needs to be added, the glass powder can be "enhanced" with copper or other metal oxides as well as elements such as sodium, calcium, potassium etc.

The second heating process can be repeated three to four times, even applying different mixtures.<ref>{{cite journal| last = Milisenda| first=C C| title=Rubine mit bleihaltigen Glasern gefullt| journal=Zeitschrift der Deutschen Gemmologischen Gesellschaft| volume=54 |issue=1| pages=35–41|publisher=Deutschen Gemmologischen Gesellschaft|year=2005|language=de}}</ref> When jewelry containing rubies is heated (for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond.

The treatment can be identified by noting bubbles in cavities and fractures using a 10× loupe.<ref>{{cite news |work= GIA Global Dispatch |publisher= Gemological Institute of America |date=16 February 2012 |url= http://www.gia.edu/research-resources/news-from-research/gia-global-dispatch/index.html |title= Lead Glass-Filled Rubies |url-status=dead |archive-url=https://web.archive.org/web/20120614070635/http://www.gia.edu/research-resources/news-from-research/gia-global-dispatch/index.html |archive-date= 14 June 2012 |access-date=22 January 2020|df= mdy-all }}</ref>

==Synthesis and imitation==
{{multiple image |direction=vertical
|image1=Artificial ruby hemisphere under a normal light.jpg
|image2=Artificial ruby hemisphere under a monochromatic light.jpg
||caption2=Artificial ruby under a normal light (top) and under a green laser light (bottom). Red light is emitted.}}
In 1837, Gaudin made the first synthetic rubies by fusing [[potash alum]] at a high temperature with a little chromium as a pigment. In 1847, [[Jacques-Joseph Ebelmen|Ebelmen]] made white sapphire by fusing [[alumina]] in boric acid. In 1877, [[Edmond Frémy]] and industrial glass-maker Charles Feil made crystal [[corundum]] from which small stones could be cut. In 1887, Fremy and [[Auguste Verneuil]] manufactured artificial ruby by fusing BaF{{sub|2}} and Al{{sub|2}}O{{sub|3}} with a little chromium at [[Incandescence|red heat]].

In 1903, Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process, later also known as the [[Verneuil process]].<ref>{{cite web|url = http://www.farlang.com/gemstones/bahadur_handbook_of_precious_stones/page_067|title = Bahadur: a Handbook of Precious Stones|year = 1943|access-date = 19 August 2007|url-status = live|archive-url = https://web.archive.org/web/20070927020704/http://www.farlang.com/gemstones/bahadur_handbook_of_precious_stones/page_067|archive-date = 27 September 2007|df = mdy-all}}</ref> By 1910, Verneuil's laboratory had expanded into a 30 furnace production facility, with annual gemstone production having reached {{convert|1000|kg|lb|-3}} in 1907.

Other processes in which synthetic rubies can be produced are through [[Czochralski process|Czochralski's pulling process]], flux process, and the [[hydrothermal synthesis|hydrothermal process]]. Most synthetic rubies originate from flame fusion, due to the low costs involved. Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curved [[Striation (geology)|striae]] and gas bubbles. The fewer the number and the less obvious the imperfections, the more valuable the ruby is; unless there are no imperfections (i.e., a perfect ruby), in which case it will be suspected of being artificial. [[Dopant]]s are added to some manufactured rubies so they can be identified as synthetic, but most need [[gemology|gemological]] testing to determine their origin.

Synthetic rubies have technological uses as well as gemological ones. Rods of synthetic ruby are used to make [[ruby laser]]s and [[maser]]s. The first working laser was made by [[Theodore Maiman|Theodore H. Maiman]] in 1960.<ref name="maiman">{{cite journal |last=Maiman |first=T.H. |author-link=Theodore Harold Maiman |year=1960 |title=Stimulated optical radiation in ruby |journal=Nature|volume=187 |issue=4736 |pages=493–494 |doi=10.1038/187493a0 |bibcode=1960Natur.187..493M|s2cid=4224209 }}</ref> Maiman used a solid-state light-pumped synthetic ruby to produce red laser light at a wavelength of 694 nanometers (nm). Ruby lasers are still in use.

Rubies are also used in applications where high hardness is required such as at wear-exposed locations in mechanical clockworks, or as scanning probe tips in a [[coordinate measuring machine]].{{citation needed|date=May 2022}}

Imitation rubies are also marketed. Red [[spinel]]s, red [[garnet]]s, and colored glass have been falsely claimed to be rubies. Imitations go back to Roman times and already in the 17th century techniques were developed to color foil red—by burning scarlet wool in the bottom part of the furnace—which was then placed under the imitation stone.<ref>{{cite web|url = http://www.farlang.com/gemstones/nicols-history-gemstones/page_036|title = Thomas Nicols: A Lapidary or History of Gemstones|year = 1652|access-date = 19 August 2007|url-status = live|archive-url = https://web.archive.org/web/20070819165714/http://www.farlang.com/gemstones/nicols-history-gemstones/page_036|archive-date = 19 August 2007|df = mdy-all}}</ref> Trade terms such as [[balas ruby]] for red spinel and [[rubellite]] for red [[tourmaline]] can mislead unsuspecting buyers. Such terms are therefore discouraged from use by many gemological associations such as the Laboratory Manual Harmonisation Committee (LMHC).

==Records and famous examples==
[[Image:NMNH-Rubies-CroppedRotated.png|thumb|Rubies at the [[National Museum of Natural History]], [[Washington, D.C.]], USA]]
* The Smithsonian's [[National Museum of Natural History]] in Washington, D.C. has some of the world's largest and finest ruby gemstones. The {{convert|23.1|carat|g|adj=on}} Burmese ruby, set in a platinum ring with diamonds, was donated by businessman and philanthropist [[Peter Buck (restaurateur)|Peter Buck]] in memory of his late wife Carmen Lúcia. This gemstone displays a richly saturated red color combined with an exceptional transparency. The finely proportioned cut provides vivid red reflections. The stone was mined from the [[Mogok]] region of [[Burma]] (now [[Myanmar]]) in the 1930s.<ref>{{cite web |url=http://www.mnh.si.edu/exhibits/ruby/index.htm |title=The Carmen Lúcia Ruby |access-date=28 February 2008 |work=Exhibitions |url-status=dead |archive-url=https://web.archive.org/web/20080309050010/http://www.mnh.si.edu/exhibits/ruby/index.htm |archive-date=9 March 2008  }}</ref>
* In 2007, the London jeweler [[Garrard & Co]] featured a heart-shaped 40.63-carat ruby on their website.<ref>{{cite web |url=http://www.garrard.com/treasures/ |title=Garrards – Treasures (large and important jewelry pieces) |access-date=8 November 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120729020054/http://www.garrard.com/treasures/ |archive-date=29 July 2012  }}</ref>
* On 13/14 December 2011, [[Elizabeth Taylor]]'s complete jewelry collection was auctioned by [[Christie's]]. Several ruby-set pieces were included in the sale, notably a ring set with an 8.24 ct gem that broke the 'price-per-carat' record for rubies ([[United states dollar|US$]]512,925 per carat – i.e., over US$4.2 million in total),<ref>[http://www.christies.com/about/press-center/releases/pressrelease.aspx?pressreleaseid=5294 The Legendary Jewels, Evening Sale & Jewelry (Sessions II and III) | Press Release | Christie's] {{webarchive|url=https://web.archive.org/web/20120129030559/http://www.christies.com/about/press-center/releases/pressrelease.aspx?pressreleaseid=5294 |date=29 January 2012 }}. Christies.com (14 December 2011). Retrieved on 2012-07-11.</ref> and a necklace<ref>[https://news.yahoo.com/photos/elizabeth-taylors-ruby-diamond-necklace-gift-mike-todd-photo-101745840.html Elizabeth Taylor's ruby and diamond necklace] {{webarchive|url=https://web.archive.org/web/20160305041651/http://news.yahoo.com/photos/elizabeth-taylors-ruby-diamond-necklace-gift-mike-todd-photo-101745840.html |date=5 March 2016 }}. News.yahoo.com (7 September 2011). Retrieved on 2012-07-11.</ref> that sold for over US$3.7 million.
* The [[Liberty Bell Ruby]] is the largest mined ruby in the world. It was stolen in a heist in 2011.<ref>{{cite web |url=http://philadelphia.cbslocal.com/2012/01/09/irreplaceable-2-million-ruby-stolen-in-wilmington-jewelry-heist/ |title='Irreplaceable' $2 Million Ruby Stolen In Wilmington Jewelry Heist |date=9 January 2012 |access-date=17 March 2017 |url-status=live |publisher=CBS Philly |archive-url=https://web.archive.org/web/20161229181248/http://philadelphia.cbslocal.com/2012/01/09/irreplaceable-2-million-ruby-stolen-in-wilmington-jewelry-heist/ |archive-date=29 December 2016  }}</ref>
* The [[Sunrise Ruby]] was the world's most expensive ruby, most expensive colored gemstone, and most expensive gemstone other than a diamond when it sold at auction in Switzerland to an anonymous buyer for US$30 million In May 2015.<ref name=BBC>{{cite news|title=World's most expensive coloured gem sells for $30m|url=https://www.bbc.co.uk/news/world-europe-32717029|access-date=13 May 2015|work=BBC|date=13 May 2015|url-status=live|archive-url=https://web.archive.org/web/20150513063509/http://www.bbc.co.uk/news/world-europe-32717029|archive-date=13 May 2015}}</ref>
* A synthetic ruby crystal became the gain medium in the world's first optical laser, conceived, designed and constructed by [[Theodore Maiman|Theodore H. "Ted" Maiman]], on 16 May 1960 at Hughes Research Laboratories.
:The concept of electromagnetic radiation amplification through the mechanism of [[stimulated emission]] had already been successfully demonstrated in the laboratory by way of the [[maser]], using other materials such as ammonia and, later, ruby, but the [[ruby laser]] was the first device to work at optical (694.3&nbsp;nm) wavelengths. Maiman's prototype laser is still in working order.{{citation needed|date=September 2024}}

[[File:Ruby Eye Pendant.jpg|thumb|right|The Ruby Eye Amulet from Mesopotamia, Adilnor Collection, Sweden.]]

==Historical and cultural references==
* The [[Old Testament]] of the [[Bible]] mentions ruby many times in the [[Book of Exodus]], and many times in the [[Book of Proverbs]], as well as various other times. It is not certain that the Biblical words mean 'ruby' as distinct from other jewels.{{Citation needed|date=January 2023}}
* An early recorded transport and trading of rubies arises in the literature on the [[North Silk Road]] of China, wherein about 200 [[Before Christ|BC]] rubies were carried along this ancient [[trackway]] moving westward from China.<ref>C. Michael Hogan, [http://www.megalithic.co.uk/article.php?sid=18006 Silk Road, North China] {{webarchive|url=https://web.archive.org/web/20131002140921/http://www.megalithic.co.uk/article.php?sid=18006 |date=2 October 2013 }}, The Megalithic Portal. 19 November 2007</ref>
* Rubies have always been held in high esteem in Asian countries. They were used to ornament armor, scabbards, and harnesses of noblemen in India and China. Rubies were laid beneath the foundation of buildings to secure good fortune to the structure.<ref>{{cite book |last1=Smith |first1=Henry G. |title=Gems and precious stones : with descriptions of their distinctive properties, the methods for determining them, &c |date=1896 |publisher=Sydney, Australia : Charles Potter |page=22 |url=https://archive.org/details/gemspreciousston00smitrich/page/22/mode/2up}}</ref>
* A traditional [[Hindu]] astrological belief holds rubies as the "gemstone of the [[Sun]] and also the heavenly deity [[Surya]], the leader of the nine heavenly bodies ([[Navagraha]])." The belief is that worshiping and wearing rubies causes the Sun to be favorable to the wearer.<ref name="smith">{{cite book|last = Smith|first = Henry G.|title = Gems and Precious Stones|publisher = Charles Potter Government Printer, Australia|year = 1896|url = http://www.farlang.com/gemstones/smith-gems-prec-stones/page_028|chapter = Chapter 2, Sapphires, Rubies|url-status = live|archive-url = https://web.archive.org/web/20070929090904/http://www.farlang.com/gemstones/smith-gems-prec-stones/page_028|archive-date = 29 September 2007|df = mdy-all}}</ref>
* In the Marvel comic books, the Godstone is a ruby that the son of J. Jonah Jameson, John Jameson found on the Moon that becomes activated by moonlight, grafts itself to his chest which turns him into the Man-Wolf.

==See also==
{{Portal|Minerals}}
*[[Anyolite]]
*[[List of individual gemstones]]
*[[List of minerals]]
*[[Shelby Gem Factory]]
*[[Verneuil process]]
*[[Emerald]]

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

==External links==
{{Commons category}}
* [http://www.gemstone.org/gem-by-gem/english/ruby.html International Colored Stone Association's ruby overview page]
* [http://webmineral.com/data/Corundum.shtml  Webmineral crystallographic and mineral info]

{{Jewellery}}
{{Gemstone}}
{{Authority control}}

[[Category:Aluminium minerals]]
[[Category:Oxide minerals]]
[[Category:Superhard materials]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 167]]
[[Category:Luminescent minerals]]
[[Category:Corundum gemstones]]