Pigeon blood red & Royal blue - SSEF · Royal blue criteria: Spectral criterion for “Royal...

GAHK Seminar March 2017| Page 0

Pigeon blood red & Royal blue:

Working towards an international standard

PDDr.MichaelS.Krzemnicki,SwissGemmologicalIns:tuteSSEFwww.ssef.ch

Photo©M.S.KrzemnickiandSSEF,exceptwhereindicatedotherwise

GAHK Seminar March 2017 | Page 1

Contents

1)Background

2)Workingtowardsaninterna:onalstandard:

TheharmonisedcriteriaofSSEFandGGL

3)Levelsofcriteria?

4)Crea:onofaninternalstandard

5)PigeonbloodredandRoyalblue:

Detailedexplana:onoftheSSEFcriteriawithspecialfocusonPigeonbloodred

6)Conclusions

7)Outlook


Background

Thecolourofcorundumismainlyrelatedtothe

presenceofcolouringelements(andoccasionally

so-calledcolourcentres)initscrystalstructure.

Thecolourweseeisresul:ngfromtheinterac:on

ofelectronsofthesecolouringelements(and

colourcentres)withlightphotons(energy)when

exposedtoalightsource.Corundum:thebeautyofcolours

Colour=selec:veabsorp:on±emission(fluorescence)


Background

-  Pigeonbloodredandroyalbluearetradecolourterms

-  notscien:fically(colorimetric)definedterms

-  sofarnointerna/onalstandard

-  strongdemandbythetradeforanindependentassessmentofcolourandtomen:oncolour

termsonlaboratoryreports

-  newtermsemerge(royalred,dragonred,Mekongwhiskyyellow,etc...)

-  historicallyperceivedasveryrareandexcep/onalinquality

-  impactonvalue

Photo©Chris7e‘s


Background

References:

Theruby...wasgenerallyofcarmine,cochineal,orrose-

redcolour,withaplayofviolet;butthemostvaluable

wasthecolourofpigeon‘sblood.

Tradi:onally,theBurmesehavereferredtothefinesthueofrubyas"pigeon'sblood"(ko-twe),a

termwhichmaybeofChineseorAraborigin.

...Itmustbestressedthatthetruepigeon‘s-bloodredisextremelyrare,moreacolourofmindthan

thematerialworld.

"...askingtoseethepigeon'sbloodislikeaskingtoseethefaceofGod.“

Somehavecomparedthiscolortothecenterofalivepigeon'seye(Brown&Day,1955).

…thecolormostcovetedtodayisthatakintoaredtrafficsignalorstoplight.Itisaglowingredcolor,

duetothestrongredfluorescenceofBurmeserubies...

…TheBurmesematerialischrome-rich,whichgivesrisetostrong

fluorescencetoultravioletradia:onandacharacteris:c

absorp:onspectrum,aswellastothe„pigeon‘sblood“colour

associatedwithBurmesestones. Excerptfrompage217:

Keller(1983),Gems&Gemology,Vol.19,No.4,209-219.

Excerptsfrompages329-330:

Hughes(1997),Ruby&Sapphire.511pages.

1888

Excerptfrompage273:

Gordon(1888).OntheRubyMinesnearMogok,Burma

1983

1997


Workingtowardsaninterna/onalstandard

TheharmonisedcriteriaofSSEFandGGL:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Press release:

Switzerland’s SSEF and Gübelin Gem Lab agree

to harmonise ‘pigeon blood red’ and ‘royal blue’ standards

The Swiss-based Gübelin Gem Lab and Swiss Gemmological Institute SSEF,

recognised as the leading laboratories for coloured stone testing, have agreed to

harmonise their standards for the colour terms “pigeon blood red” and “royal blue.”

Their goal is to standardise the usage of these terms for the benefit of the international

gemstone trade.

The colour terms “pigeon blood red“ and “royal blue“ have been used for centuries by

the trade to describe, respectively, only the finest quality rubies and sapphires, which

aside from their distinct colours, invariably are stones of superior quality, and hence are

among the most coveted gems.

SSEFandGübelinGemlabusetheterms

pigeonbloodredandroyalblueonlyforrubiesandsapphires:

-  whichexhibitstrongredorbluecoloursatura:on

-  whichareuntreated

-  whichmeetspecificchemicalandspectroscopiccharacteris:cs

-  offinequalityintermsofinclusions,transparency,andcolourhomogeneity

Butfinallytheyarecolourtermsandthusassessedusingmastersetsofrubiesand

sapphiresaccordingtoaninternallaboratoryprotocol.

JointPressreleaseofSSEF&GGL1.Nov2015

Seewww.ssef.ch,Pressreleases


Levels of criteria ?

-  shouldthesetermsjustbeusedasgeneric

colourterms?

-  orshouldtherebeaddi:onalcriteria(levels)

toqualifyforthesetwocolourterms?

Pagoda

Wikipedia:Apagodaisa7eredtowerwith

mul7pleeaves,builtintradi7onsorigina7ngas

stupainhistoricSouthAsia.

Mainques/on:“Pagoda-principle”yesorno?


Levels of criteria ?

Ifweaccept,thatfurtherajributesarerequired,thentheonlyques:oniswheretosetthelimits.

-  forimita/onsorothergems?

-  forsynthe/crubyorsapphire?

-  fortreatedrubiesandsapphires?

-  linkedtoqualityrequirements(transparency,colourhomogeneityetc.)?

-  linkedtochemical/spectralspecifica:ons(influencingcolour)?

Flowchartoftreatmentop7onsforruby.©M.S.Krzemnicki

Shouldthesecolourtermsbeapplicable:


Creation of an internal standard

Laboratorieshavetocreateinternalstandardstobeabletocorrectlyandconsistently

describegemmaterialsontheirlabreports.

Suchaninternalstandardmaybecomeinterna:onallyaccepted/harmonised(e.g.CIBJO,

LMHC,SSEF-GübelinGGL...).

RedspinelonSSEFGemstoneReport

Example:Fancycoloureddiamonds

GIAhasdefactocreateda„standard”terminologywhichtodayisgloballyacceptedinthe

trade.



Examples:

-  Ruby/pinksapphire

-  Padparadscha

-  Paraibatourmaline/lightbluetourmaline(withCutraces)

-  Emerald/greenberyl(withCrtraces)

-  Colourchangeorjustslightcolourshipunderdifferentlightsources

-  Pearlcolours

Padparadschayesorno?



Paraibatourmaline lightbluetourmaline(withCutraces)



Thecolourgradingofrubyandsapphireismuchmore

complexthanfordiamonds.

Takingtheexampleofthetermpigeonbloodred,thenext

slidesshowourcriteriawhicharerequiredtoqualifyforthis

term.

Ourcriteriaforroyalblueareverysimilartotheonesof

pigeonbloodred,onlydifferinginthespectroscopic

(chemical)specifica:on.

Colourexamplesofpinksapphiretoruby


Pigeon blood red

Harmonised criteria (SSEF & GGL):

Thefundamentalcriterioniscolour:

Thecolourofarubyisgradedbycomparisonwithamastersetof(natural)rubies.

Themainparametershue,satura:onandbrightnessareobserved.

Onlyrubieswithastrongsatura:onanda“vivid”redcolour(similartoredtrafficlight)withno

oronlyslightpurplishcolour:ntareaccepted.

RubymastersetforpigeonbloodredofSSEF

Pigeonbloodred notPigeonbloodrednotPigeonbloodred


Pigeon blood red

criteria:

Colourobserva/on:

Basedonthreefactors:

1)  Lightsource(emissioncharacteris:cs)

2)  Observer(protocolandtraining)

3)  Observeditem(e.g.rubyorsapphire)

Togradecolourconsistently,thefirsttwofactorshavetobedefinedandstandardisedasmuchas

possible.

CIEChroma7citydiagram

Munsellcolourspaceandcharts


Pigeon blood red

criteria:

Effectoflighttemperatureoncolourappearance:

TworubiesshowingweakandstrongLWUVreac:onunderdifferentlightsources.

Spectraldistribu7onofD50illuminant,

comparedtohalogenandfluorescentlight.

LWUV D65(6500K)daylight A(2800K)incandescentlight


Pigeon blood red

criteria:

Standardizedcolourobserva/on:

-  Colourobserva:onfromthetop

-  Rubyslightly:lted20°inalldirec:ons

-  Standardisedlight(ideallycon:nuum,e.g.

filteredhalogenlampequivalenttoCIED50

illuminant,99+colourrenderingefficiency).

-  Therubyandthemasterstonesareplaced

directlybelowthelightsourceatapprox.20cm

distance.Lightintensityatthatpointapprox.

2200lux(sameasfordiamondsPAS1048.2,

§5.3.8,page5).

Spectraldistribu7onofD50illuminant,

comparedtohalogenandfluorescentlight.

ComparisonofD65(diamond)andD50


Pigeon blood red

criteria:

Fluorescence:

Thebodycolourofpigeonbloodredrubiesiscomplementedbyastrongfluorescencewhen

exposedtoultravioletlight(LWUV:strong,SWUV:medium–mediumweak).


Pigeon blood red

criteria:

Fluorescence:

Thefluorescenceiscausedbyhigh

chromiumcontentcombinedwith

lowironcontent.Itresultsina

dis:nct"innerglow"whenexposed

tosunlight(whichcontainsUV),an

effectwhichhasbeencovetedinthe

tradehistorically.

Innerglow

strongUVreac7on

Noinnerglow

weakUVreac7on

Rubieswithveryhighchromiumcontentandlowironconcentra:onhowevershow

reducedfluorescenceanddonotqualify.


Pigeon blood red

criteria:

Chemicalcomposi/on:

Generallyonlyrubieswithverylowamountofiron(comparedtochromium)showfluorescence

intensitywhichmeetsourcriterionforpigeonbloodred.

Thechemicalcriterioncommonlyismetforrubieswhichformedinmarbledeposits,suchasin

Myanmar,Vietnam,Tajikistan,Afghanistan,Tanzania(e.g.Morogoro),Kenya,etc.

0.000

0.200

0.400

0.600

0.800

1.000

1.200

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900

Ironconcentra*on(wt%

Fe2O3)

Chromiumconcentra*on(wt%Cr2O3)

Afghanistan Burma EastAfrica Madagascar Mozambique Siam Tajikistan Vietnam Winza,Tanzania

0.000

0.200

0.400

0.600

0.800

1.000

1.200

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900

Ironconcentra*on(wt%

Fe2O3)

Chromiumconcentra*on(wt%Cr2O3)

Afghanistan Burma EastAfrica Madagascar Mozambique Siam Tajikistan Vietnam Winza,Tanzania

Cr2O3=Fe2O3

pigeonbloodredbasedonourcriteria


Royal blue

criteria:

Thefundamentalcriterioniscolour:

Thecolourofasapphireisgradedbycomparisonwithamastersetof(natural)sapphires.

Themainparametershue,satura:onandbrightnessareobserved.

Onlysapphireswithastrongsatura:onanda“vivid”bluecolourbutnoaddi:onalcolour:nt

(greenish,greyishorpurple)areaccepted.

SapphiremastersetforroyalblueofSSEF.

Royalblue notRoyalbluenotRoyalblue


Royal blue

criteria:

Spectralcriterionfor“Royalblue”:

-  Blueofstrongsatura:on,eitherpureorwithaveryslightpurplish:nt.

-  historicallycoinedforthebestqualityofsapphiresorigina:ngfromtheMogokareainBurma,itis

alsoappliedbySSEF&GGLforsapphiresfromothermetamorphicdeposits,suchasinMadagascar,

SriLanka,andKashmir.

-  UV-Visabsorp:onspectrumdominatedbyFe2+-Ti4+Intervalencechargetransfer.

AvaSoft 7.4 Sapphire, Sri Lanka

Wavelength [nm]750700650600550500450400350300

Abso

rbance

[A

.U]

1

0

© Swiss Gemmological Institute SSEF

MetamorphicsapphireAvaSoft 7.4 Sapphire Basaltic deposit

Wavelength [nm]700650600550500450400350

Ab

sorb

an

ce [

A.U

]

1

0

© Swiss Gemmological Institute SSEF

Fe2+-Fe3+IVCT

Fe2+-Ti4+IVCTFe3+

Absorbance

Absorbance

Basal/csapphire

basal7c metamorphic


Pigeon blood red

criteria:

Treatment:

Onlyrubieswhichshownoindica:onsofany

treatment.

Basedonthehistoricalconnota:onofrarity

andexcep:onalquality.

Photo©Dreams7me.comPhoto©Twobadcats,www.etsy.com

Glassyresidues(borax)inhealedfissureofheatedruby

fromSiam.


Pigeon blood red

criteria:

Pleochroism:

Differenttodiamond,ruby(andsapphire)is

op:callyanisotropicandshowsadis:nctpleochroism.

ruby: o-ray purplishred

e-ray slightlyorangered

Lamellartwinningrevealingthepleochroic

coloursofruby.Photo©H.A.Hänni


Pigeon blood red

criteria:

Pleochroism:

Theperceivedcolourofarubyisaninterplayofits

pleochroiccolours.

Itisdependentfromtheorienta:oninwhichthe

gemstonehasbeencutfromtheroughcrystalandthe

orienta:onitislookedat.

©R.Scoh,Jewelery-Secrets.com

SSEF&GGL:

-  Colourobserva:onfromthetop

-  Rubyslightly:lted20°inalldirec:ons


Pigeon blood red

criteria:

Propor/ons:

Verydifferenttodiamonds,rubies(andsapphires)arerarelycutin“ideal”propor:onswhich

wouldmaximizetheyieldofinternallyreflectedlight(whenviewedthroughthetable).

Theircutisratherreflec:ngtheshapeoftheroughandweightconsidera:ons,openresul:nga

transmission“window”,whichmay–incombina:onwithpleochroism–stronglycontributeto

thevisualappearanceofthestone.

min. ~ 30 %


Pigeon blood red

criteria:

Zoning:

Rubies(andsapphires)openshowcolourzoning,

i.e.varia:onsincoloursatura:on.

Ifcutproperly,theeffectofsuchzoningmightbe

minimisedwhenviewedfromthetop.

Pigeonbloodredonlyforrubieswithnoto

insignificantzoningwhenviewedfromthetop.

Twoexamplesofrubieswithstrongcolour

zoningnotfiingforpigeonbloodred.


Pigeon blood red

criteria:

Colourmodifier:

Rubiesopencontainfissuresorcavi:esfilled

withorangesubstancesuchasironhydroxide

orevenorangeoil.

Althoughonlylocallypresent,suchcolour

modifiermayshipthecolourofastone

considerably.

Pigeonbloodredtermnotapplicableforsuch

stones.

Orangefissurefillinginarubyshijingits

originallypurplishredbodycolourintored.


Pigeon blood red

criteria:

Orangefissurefillinginarubyshijingits

originallypurplishredcolourintored.

Colourmodifier:

Similarsitua:onalsoincaseofthispinksapphire

whichdoesnotqualifyforpadparadscha.


Pigeon blood red

criteria:

Thesecolourlessinclusionsandtheweak“silk”in

zonesdonotaffecttheperceivedcolourofthisruby.

Inclusions:

Theymustberela:velyfreeofeye-visible

ordarkinclusionswhenviewedfromthe

topwithapprox.20cmdistancetothe

ruby.

Inclusionsandweaktomedium“silk”in

zoneswhichdonot(oronlyslightly)

affectperceivedcolourareacceptable.


Pigeon blood red

criteria:

Transparency:

Rubymustshowvividinternalreflec:ons.

TheStarofKashmir(approx.20ct)

„sleepy“ „vivid“internalreflec:ons


Conclusions

-  Thetradetermspigeonbloodredandroyalbluehistoricallyarenotusedaspurecolour

termsbutlinkedtorarityandexcep/onalquality.Thisconnota:onmakesthesetermsso

valuableforthetradeandconsumers.

-  SSEFandGübelinGGLhaveharmonisedtheircriteriain2015.Butresultsmays:lldiffer,as

colourgradingisfinallyanindependentopinionofeachlaboratory(similartodiamond

grading).

-  Colourgradingisfollowingainternallystandardisedprotocol.

-  Onlyforrubies/sapphiresfizngallcriteria

-  Onlyarestrictednumberofrubies/sapphiresareajributedthecolourgrades“pigeonblood

red”or“royalblue”basedonthepresentedstrictcriteria.


Conclusions

Summaryofourcriteria:

-  Astrongredorbluecolour(comparedtomasterstones)

-  Onlyforrubiesandsapphiresformedinnature

-  Onlyforuntreatedrubiesandsapphires

-  Specificchemicalandspectroscopicproper:esrelatedtocolourappearance

(e.g.fluorescenceinrubies,par:altransmissionintheredforsapphires)

-  Notrestrictedtoasinglesource,butrathertoageologicalsezng

-  Homogeneityofcolour(orienta:onofcut,pleochroism)

-  Goodpropor:ons,avoidingdominant“windowsitua:on”

-  Noapparentcolourzoning

-  Nocolourmodifierbyfissurefillings

-  Noapparentanddisturbinginclusions

-  Goodtransparency,dis:nctinternalreflec:ons

-  Colourgradingisfollowingainternallystandardisedprotocol.

-  Weusea5000KD50daylightequivalentillumina:on(con:nuum)

-  Minimum“4-Eyes”principle



Outlook:

Directlinkfordownload:

www.ssef.ch/fileadmin/Documents/PDF/650_Presenta/ons/2016_CIBJO_colourterms_SSEF.pdf

Openaccesstocriteria

Downloadaslightlymodifiedversionof

thispresenta:ononourSSEFwebsite.

www.ssef.ch



Outlook:

CIBJOWorldJewelleryFedera:on:

Invitedspeakerandpresenta:onofcriteriaata

SpecialSessionoftheCIBJOCongressinYerewan

(Armenia),October2016.



Outlook:

-  Weareconvincedthatstandardisingandharmonisingtheuseofthesecolourtermsis

importantforthetradeandlaboratories.

-  TheSSEF&GübelinGGLharmonisa:onofcriteriamaybeconsideredafirststepinthis

direc:on.

-  Anyorganisa:on/laboratorywhichwouldliketojointhisharmonisa:oniswelcome.

-  Wearereadytoduplicateourrubyandsapphiremastersetsfororganisa:ons,laboratoriesand

trademembers.

GAHK Seminar March 2017| Page 35

Thank you for your attention!

Highlyajrac:vepinkishredcolour!

The„QueenofBurma“(23ct)

soldforUS$6mioatChris:e‘sGeneva,2014.

Pigeon blood red & Royal blue - SSEF · Royal blue criteria: Spectral criterion for “Royal...

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