Editing Carat (mass)

{{Short description|Unit of mass}}
{{About|the unit of mass used for gemstones and pearls|the purity scale used for gold|Fineness#Karat}}
 {{Other uses|carat (disambiguation)||karat (disambiguation)}}
{{Infobox unit
| name         = carat
| image        = One carat brilliant.jpg
| caption      = A {{cvt|1|carat|mg|adj=on}} [[brilliant (diamond cut)|brilliant]] [[diamond]]
| standard     =
| quantity     = 
| symbol       = ct
| symbol2      = 
| namedafter   = 
| extralabel   = 
| extradata    = 
| units1       = [[milligrams]]
| inunits1     = 200
| units_imp1   = [[ounces]]
| inunits_imp1 = 0.00705
}}
{{diamond}}
[[File:Diamond Balance Scale 0.01 - 25 Carats Jewelers Measuring Tool.jpg|thumb|Diamond-weighing kit, with weights labelled in grams and carats]]

The '''carat''' ('''ct''') is a [[units of measurement|unit]] of [[mass]] equal to {{cvt|200|mg|oz ozt|lk=on|5}}, which is used for measuring [[gemstone]]s and [[pearl]]s.
The current definition, sometimes known as the '''metric carat''', was adopted in 1907 at the Fourth [[General Conference on Weights and Measures]],<ref name= "Science1908">{{cite book| title= Science| url= https://books.google.com/books?id=D5YCAAAAYAAJ&pg=PA144|access-date=30 June 2012|year=1908|publisher= [[American Association for the Advancement of Science]] |page= 144}}</ref><ref name="CGPM4" /> and soon afterwards in many countries around the world.{{efn-lr|The [[United States]] adopted the metric carat definition on July 1, 1913, the [[United Kingdom]] on 1 April 1914.}} The carat is divisible into 100 ''points'' of 2&nbsp;mg. Other subdivisions, and slightly different mass values, have been used in the past in different locations.

In terms of [[diamond]]s, a [[Paragon (diamond)|paragon]] is a flawless stone of at least 100 carats (20&nbsp;g).<ref name=ahdparagon>{{cite book|title=American Heritage Dictionary of the English Language|year=2013|publisher=Houghton Mifflin Harcourt|url=https://www.ahdictionary.com/word/search.html?q=paragon|access-date=2013-12-24|archive-url=https://web.archive.org/web/20160809232409/https://ahdictionary.com/word/search.html?q=paragon|archive-date=2016-08-09|url-status=dead}}</ref>

The [[American National Standards Institute|ANSI]] [[Electronic Data Interchange|X.12 EDI]] standard abbreviation for the carat is '''CD'''.<ref>{{cite web | url= https://das.ct.gov/Purchase/Info/ANSI_UNITS_OF_MEASURE.pdf |title= ANSI Units of Measure| website= das.ct.gov| publisher= Dept. of Admin. Services, State of Connecticut| archive-url= https://web.archive.org/web/20120417021447/https://das.ct.gov/Purchase/Info/ANSI_UNITS_OF_MEASURE.pdf |archive-date=April 17, 2012 | url-status= dead}}</ref>

==Etymology==
First attested in English in the mid-15th century, the word ''carat'' comes from Italian ''carato'', which comes from [[Arabic language|Arabic]] (''qīrāṭ''; قيراط), in turn borrowed from [[Greek language|Greek]] ''kerátion'' κεράτιον '[[carob]] seed',<ref name=harper>{{OEtymD|carat|accessdate=}}</ref><ref name=Liddel>{{cite encyclopedia| url= https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dkera%2Ftion| title= κεράτιον| first1= Henry George| last1= Liddell| first2= Robert| last2= Scott| encyclopedia= A Greek-English Lexicon| via= Perseus.Tufts.edu| access-date= 2021-02-20| archive-date= 2022-12-30| archive-url= https://web.archive.org/web/20221230220752/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dkera%2Ftion| url-status= live}}</ref><ref>{{cite encyclopedia | first= Walter W.| last= Skeat| year= 1888| url= https://archive.org/details/etymologicaldict00skeauoft | title= carat | encyclopedia= An Etymological Dictionary of the English Language| publisher= Henry Frowde| place= London| pages= 93–94}}</ref> a diminutive of ''keras'' 'horn'.<ref>{{cite encyclopedia| url= https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dke%2Fras| title= κέρας| first1= Henry George| last1= Liddell| first2= Robert| last2= Scott| encyclopedia= A Greek-English Lexicon| via= Perseus.Tufts.edu| access-date= 2021-02-20| archive-date= 2012-10-08| archive-url= https://web.archive.org/web/20121008220111/http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry=ke%2Fras| url-status= live}}</ref> It was a unit of weight, equal to 1/1728 (1/12{{sup|3}}) of a pound (see [[Mina (unit)]]).<ref name=Liddel/><ref>{{cite encyclopedia| url= https://oxforddictionaries.com/view/entry/m_en_gb0122990#m_en_gb0122990 | archive-url= https://web.archive.org/web/20100824022152/http://www.oxforddictionaries.com/view/entry/m_en_gb0122990#m_en_gb0122990 | url-status= dead | archive-date= August 24, 2010 |title= carat| encyclopedia= Oxford Dictionaries| via=oxforddictionaries.com }}</ref><ref name=harper/>

==History==
Carob seeds have been used throughout history to measure jewelry, because it was believed that there was little variance in their mass distribution.<ref>{{cite web|last1=Naturski|first1=Sebastian|title=Carat Weight|url=https://yourdiamondteacher.com/diamond-4cs/carat-weight/|website=Your Diamond Teacher|access-date=3 March 2017}}</ref> However, this was a factual inaccuracy, as their mass varies about as much as seeds of other species.<ref>{{Cite journal | last1 = Turnbull | first1 = L. A. | last2 = Santamaria | first2 = L. | last3 = Martorell | first3 = T. | last4 = Rallo | first4 = J. | last5 = Hector | first5 = A. | title = Seed size variability: From carob to carats | journal = Biology Letters | volume = 2 | issue = 3 | pages = 397–400 | year = 2006 | pmid = 17148413 | pmc = 1686184 | doi = 10.1098/rsbl.2006.0476}}</ref>

In the past, each country had its own carat. It was often used for weighing [[gold]]. Beginning in the 1570s, it was used to measure weights of [[diamond]]s.<ref name=harper/>

===Standardization===
An 'international carat' of 205 milligrams was proposed in 1871 by the Syndical Chamber of Jewellers, etc., in Paris, and accepted in 1877 by the Syndical Chamber of Diamond Merchants in Paris. A metric carat of 200 milligrams is exactly one-fifth of a gram and had often been suggested in various countries,<ref name="CGPM4" /> and was finally proposed by the International Committee of Weights and Measures, and unanimously accepted<ref name="CGPM4">[https://www.bipm.org/utils/common/pdf/CGPM/CGPM4.pdf#page=89 Comptes rendus des séances de la quatrième conférence générale des poids et mesures] {{Webarchive|url=https://web.archive.org/web/20220921164326/https://www.bipm.org/utils/common/pdf/CGPM/CGPM4.pdf#page=89 |date=2022-09-21 }}, 1907, page 89</ref> at the fourth sexennial General Conference of the Metric Convention held in Paris in October 1907. It was soon made compulsory by law in France, but uptake of the new carat was slower in England, where its use was allowed by the [[Weights and Measures Acts (UK)#19th century|Weights and Measures (Metric System) Act of 1897]].<ref>{{Source-attribution|sentence=yes|{{cite magazine|title=Notes on the weight of the 'Cullinan' diamond|author=Leonard J. Spencer|magazine=Mineralogical Magazine|year=1910|volume=XV|issue=71|pages=318–326|url=https://archive.org/details/NotesOnTheWeightOfTheCullinanDiamond}}}}</ref>

==Historical definitions==
{| class="wikitable floatright"
|+ Carat before 1907<ref>{{cite journal
 |title=On the origin of the carat as the unit of weight for gemstones
 |first=Tao |last=Zhengzhang |journal=Chinese Journal of Geochemistry
 |date=July 1991 |volume=10 |number=3 |pages=288–293
 |doi=10.1007/BF02843332 |s2cid=127800966 |issn=1993-0364 }}</ref>
!style="text-align:left;"| Location !!style="text-align:left;"| mg
|-
| [[Cyprus]]		|| 187
|-
| ''unknown''		|| 188.6
|-
| [[Brazil]]		|| 192.2
|-
| [[Egypt]]		|| 195
|-
| [[Ambon Island|Ambonia]] || 197
|-
| [[Florence]]		|| 197.2
|-
| International carat<br>&nbsp; [[Jakarta|Batavia]], [[Borneo]], [[Leipzig]]
|style="vertical-align:top;"| 205
|-
| [[South Africa]] (1)	|| 205.304
|-
| London-New York (1)	|| 205.303
|-
| [[Spain]]		|| 205.393
|-
| London-New York (2)	|| 205.409
|-
| [[Berlin]]		|| 205.44
|-
| [[John Law's Company|Paris, East India]] || 205.5
|-
| [[South Africa]] (2)	|| 205.649
|-
| [[Amsterdam]]		|| 205.7
|-
| [[Lisbon]]		|| 205.75
|-
| [[Frankfurt]] (on Main) || 205.77
|-
| [[Vienna]]		|| 206.13
|-
| [[Venice]]		|| 207
|-
| [[Chennai|Madras]]	|| 207.353<!-- <br>207.36 -->
|-
| ''unknown''		|| 213
|-
| [[Bucharest]]		|| 215
|-
| [[Livorno]]		|| 215.99
|}

=== UK Board of Trade ===
In the [[United Kingdom]] the original '''[[Board of Trade]] carat''' was exactly {{frac|3|1647|9691}} [[Grain (unit)|grain]]s (~3.170&nbsp;grains = ~205&nbsp;mg);{{efn-lr|The pre-1888 [[Board of Trade]] carat, of which there were exactly {{frac|151|27|64}} per [[ounce#International troy ounce|ounce troy]], was approximately {{cvt|205.4094|mg}}.}} in 1888, the Board of Trade carat was changed to exactly {{frac|3|17|101}} grains (~3.168&nbsp;grains = ~205&nbsp;mg).{{efn-lr|The post-1887 Board of Trade carat, of which there were exactly {{frac|151|1|2}}; per ounce troy, was approximately {{cvt|205.3035|mg}}.}} Despite it being a non-metric unit, a number of metric countries have used this unit for its limited range of application.

The Board of Trade carat was divisible into four ''diamond grains'',{{efn-lr|Unlike the modern carat, the Board of Trade carat was not used for measuring pearls; those were measured with ''pearl grains''.}} but measurements were typically made in multiples of {{frac||1|64}} carat.

=== Refiners' carats ===
There were also two varieties of ''refiners' carats'' once used in the United Kingdom—the '''pound carat''' and the '''ounce carat'''.{{efn-lr|The refiners' carats were the offspring of the [[carat (purity)|carat as a measure of fineness for gold]].}} The [[pound (mass)#Troy pound|pound troy]] was divisible into 24 ''pound carats'' of 240 grains troy each; the pound carat was divisible into four ''pound grains'' of 60 grains troy each; and the pound grain was divisible into four ''pound quarters'' of 15 grains troy each. Likewise, the [[ounce#International troy ounce|ounce troy]] was divisible into 24 ''ounce carats'' of 20 grains troy each; the ounce carat was divisible into four ''ounce grains'' of 5 grains troy each; and the ounce grain was divisible into four ''ounce quarters'' of {{frac|1|1|4}} grains troy each.<ref>{{cite book| last= Chaffers| first= William|author-link=William Chaffers| year= 1883| title= Hall Marks on Gold and Silver Plate| edition= 6th| place= London| publisher= Bickers & Son}}</ref>

=== Greco-Roman ===
The ''solidus'' was also a [[Roman Empire|Roman]] weight unit. There is literary evidence that the weight of 72&nbsp;coins of the type called ''[[solidus (coin)|solidus]]'' was exactly 1 [[Roman pound]], and that the weight of 1&nbsp;''solidus'' was 24&nbsp;''[[siliqua]]e''. The weight of a Roman pound is generally believed to have been 327.45&nbsp;g or possibly up to 5&nbsp;g less. Therefore, the metric equivalent of 1 ''siliqua'' was approximately 189&nbsp;mg. The Greeks had a similar unit of the same value.<ref name="grierson">{{cite journal | last=Grierson | first=Philip | title=The Monetary Reforms of 'Abd Al-Malik | journal=Journal of the Economic and Social History of the Orient | volume=3 | year=1960 | pages=241–264 | doi = 10.1163/156852060X00098 | issue=3}}</ref>

Gold [[fineness]] in [[Fineness#Karat|carats]] comes from carats and grains of gold in a solidus of coin. The conversion rates 1&nbsp;solidus = 24&nbsp;carats, 1&nbsp;carat = 4&nbsp;grains still stand.<ref>{{cite journal |last1=Harper |first1=K |title=People, Plagues, and Prices in the Roman World: The Evidence from Egypt |url=https://www.cambridge.org/core/journals/journal-of-economic-history/article/people-plagues-and-prices-in-the-roman-world-the-evidence-from-egypt/50D27EAD5045D12C1573DFFB5D5C029C |journal=The Journal of Economic History |year=2016 |volume=76 |issue=3 |pages=803–839 |publisher=Cambridge University |doi=10.1017/S0022050716000826 |access-date=16 June 2019}}</ref> Woolhouse's ''Measures, Weights and Moneys of All Nations''<ref name=":0">{{cite book| last= Woolhouse| first= W. S. B. |title= Measures, Weights and Moneys of All Nations| url= https://archive.org/details/measuresweightsm00woolrich| year=1891}}</ref> gives gold fineness in carats of 4 grains, and [[silver]] in troy pounds<ref name=":0" /> of 12&nbsp;[[troy ounce]]s of 20&nbsp;[[pennyweight]] each.{{clarify|date=January 2012|reason=Why are we citing a 100+ year old book for information on current units, in a section on ancient units?}}

== Notes== 
{{notelist-lr}}

==References ==
{{Reflist}}

{{Jewellery}}
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[[Category:Units of mass]]
[[Category:Jewellery making]]
[[Category:Metricated units]]