Where is the boundary between colour varieties of gems? (2019)

| Red Ruby or Pink Sapphire, that’s the Question W here is the boundary between colour varieties of gems?

Presentation by PD Dr Michael S. Krzemnicki, Director Swiss Gemmological Institute SSEF

Photos © M.S. Krzemnicki and SSEF, except where indicated otherwise | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 1

| CONTENTS

1) Introduction: Creation of standards and standardised procedures 2) Real cases at SSEF: -

Ruby vs Pink Sapphire Padparadscha vs Fancy Sapphires Cobalt Spinel vs Blue Spinel Emerald vs Green Beryl Alexandrite vs Chrysoberyl

3) Conclusions

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 2

| TERMS & SIGNIFICANCE Mineral: - Scientifically well defined term !

-

CNMMN (Commission on New Minerals and Mineral Names) of IMA (International Mineralogical Association)

Variety: - scientifically not well defined term !

-

Chemically related: variations of the chemical composition, mostly by element substitution(s) Colour related: variations of colour, mostly but not always linked to variations in colouring elements.

External appearance: e.g. single crystal to polycrystalline aggregates (quartz – chalcedony)

-

“Defined” by history (text books), trade organisations (CIBJO, ICA), laboratories….

-

Consumers often better know variety names than the related mineral name of gems.

Beryl colour varieties | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 3

| CREATION OF STANDARDS

Variety “definitions” commonly are rather vague and general.

As a consequence, gemmological laboratories have to create internal standards to consistently describe gem materials on their lab reports.

Such an internal standard may become internationally accepted/harmonised (e.g. CIBJO, LMHC,...).

The wheel of colour of natural corundum

Gemmological laboratories are constantly working together to further harmonise their wording. see for example LMHC infosheets: www.lmhc-gemmology.org

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 4

| STANDARDISED PROCEDURES Colour observation:

Based on three factors: 1) Light source (emission characteristics) 2) Observer (protocol, tools and training) 3) Observed item (e.g. ruby or pink sapphire) To grade colour consistently, the first two factors have to be defined and standardised as much as possible.

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 5

| STANDARDISED PROCEDURES Light source:

-

Colour observation from the top

-

Gemstone slightly tilted 10-20° in all directions

-

Standardised light (ideally continuum, e.g. filtered halogen or LED lamp equivalent to CIE D65 (at SSEF for diamonds) or CIE D50 illuminant (at SSEF for coloured gemstones) and with high colour rendering efficiency.

Spectral distribution of D50 illuminant, compared to halogen and fluorescent light.

Comparison of CIE D65 and CIE D50 | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 6

| OPTIONS TO DISTINGUISH GEMSTONE VARIETIES based on:

Colour only

or

Colour and spectroscopy (& chemistry)

or

Colour charts (e.g. Munsell, Color CodexTM…)

using:

Master stones

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 7

| RUBY vs PINK SAPPHIRE The separation of ruby vs pink sapphire is based only on the colour saturation (table up appearance).

At SSEF, we differentiate: Red Pinkish red Purplish red

ruby ruby ruby

Pink Purple

pink sapphire purple sapphire

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 8

| RUBY vs PINK SAPPHIRE Since decades, the SSEF uses a set of master stones produced and distributed in the 80ies by the ICA.

ruby

pink sapphire

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 9

| RUBY vs PINK SAPPHIRE ColorCodexTM, a new and very easy system to grade the colour of gemstones, developed by C. Smith (NYC, USA). (see www.color-codex.com)

ruby

pink sapphire

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 10

| RUBY vs PINK SAPPHIRE Zoning vs visual appearance

There is no specific chromium concentration threshold to separate ruby and pink sapphire.

Table up and table down view of a Burmese ruby with strong colour zoning

Strongly zones “Ottu” sapphire from Sri Lanka | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 11

| PADPARADSCHA Padparadscha sapphire, intermediate variety between pink sapphire and orange sapphire. The term is only based on colour.

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 12

| PADPARADSCHA Padparadscha sapphire is a variety of corundum from any geographical origin whose colour is a subtle mixture of pinkish orange to orangey pink with pastel tones and low to medium saturations when viewed in standard daylight.

Padparadscha chart, based on Munsell colour system, created by F. Notari (1996)

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 13

| PADPARADSCHA Colour measurement, using GCA instrument (in-house developed).

GCA Transmission AVERAGED Color (a*, b*) 20

15

BLUE <-- b* --> YELLOW

10

5

0

-5

-10

-15

-20 -20

-15

-10

-5

0

5

10

15

20

GREEN <-- a* --> RED

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 14

| NOT PADPARADSCHA Colour modifier:

Pink sapphire containing orange iron hydroxide. Although visually orangey pink this stone does not qualify for padparadscha.

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 15

| NOT PADPARADSCHA: UNSTABLE COLOUR

After 5 minutes “activation” using a UV lamp the colour has considerably changed.

But unfortunately this new colour will slowly fade again to pink in the coming few weeks…

This pink sapphire was submitted to us as a ‘padparadscha’ ! …so this fancy sapphire is pink again after few weeks exposure to daylight

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 16

| NOT PADPARADSCHA: UNSTABLE COLOUR slight to moderate colour shift (still padparadscha)

FEATURE ARTICLE

Absorbance (a.u.)

Figure 1: This 9.1 ct sapphire from the Ambatondrazaka area of Madagascar shows vivid pink colouration (far left).

After exposure to a long-wave UV lamp for a few minutes, the stone changed to a vivid pinkish orange typical of that shown by padparadscha sapphires (centre). With fade testing, the colour shifted back to the chromium-related pink colour (below). Composite photo by Vito Lanzafame, SSEF.

distinct to strong colour shift (not padparadscha)

500

600 Wavelength (nm)

700

Unstable Colouration of Padparadscha-like Sapphires Michael S. Krzemnicki, Alexander Klumb and Judith Braun

ABSTRACT: After the October 2016 discovery of a new gem deposit at Bemainty near Ambatondrazaka, Madagascar, a number of sapphires with padparadscha-like colour entered the trade.

However, most of these stones were found to have unstable colour, which changes from pinkish orange to more-or-less pure pink after a few weeks in daylight. In this study, the authors investigate the colour stability of padparadscha-type sapphires of metamorphic origin—mainly those originating from Madagascar (Ambatondrazaka and Ilakaka) and Sri Lanka. The 48 samples could be separated into three groups after colour-stability testing: sapphires that did not show a noticeably different appearance (case A); sapphires with a slight-to-moderate colour difference within the padparadscha range (case B); and fancy-colour sapphires showing a distinct change in appearance that fell outside of the padparadscha range (case C). The last situation was especially common for the stones from Ambatondrazaka, thus revealing that careful colour-stability testing is mandatory for proper gemmological identification of any sapphire showing a yellow to orange colour component.

Further reading: Journal of Gemmology (Gem-A) and InColor and SSEF Facette 24, 2018 https://www.ssef.ch/ssef-facette/ and new LMHC website (Infosheet 4) https://www.lmhc-gemmology.org/gemstones

The Journal of Gemmology, 36(4), 2018, pp. 346–354, http://doi.org/10.15506/JoG.2018.36.4.346 © 2018 The Gemmological Association of Great Britain

346

THE JOURNAL OF GEMMOLOGY, 36(4), 2018

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 17

| Co-SPINEL vs. BLUE SPINEL Where is the limit ?

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 18

| Co-SPINEL vs. BLUE SPINEL Cobalt as colouring element

Cobalt is known since antiquity as colouring agent. Already small traces of cobalt (Co2+) may produce an vivid (cobalt) blue colour.

Can be used to colour low quality corundum as an additive to Pb-glass treatment.

Blue Co-coloured glass bottles. © istockphotos.com

Co-treated corundum. © GIT Thailand

Roman Co-coloured perfume bottle. © scottishantiques.com | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 19

| Co-SPINEL vs. BLUE SPINEL Co-diffusion treatment of low quality spinel

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 20

| Co-SPINEL vs. BLUE SPINEL UV-Vis absorption spectroscopy

Co2+ and Fe2+ both may produce a blue colour in spinel.

Using classic ED-XRF analysis, cobalt is in most spinels below detection limit and can only be detected with absorption spectroscopy. At SSEF, the term Cobalt spinel is only used for those blue spinels in which the Co-bands dominate their spectrum.

Co-1, Co-2, Co-4, Co-5, Co-6: spectrum dominated by Co-bands Co-3, Co-7, Co-8: spectrum dominated by Fe-bands

Spectra from: Hanser C. 2013 (unpublished Bachelor thesis, University Freiburg i. Br. (Germany) in collaboration with SSEF –

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 21

| Co-SPINEL vs. BLUE SPINEL UV-Vis absorption spectroscopy

A specific concentration of Co2+ cannot be taken as a defining criterion to separate Co-spinel from blue spinels, as certain spinels distinctly dominated (in the spectrum) by iron contain higher trace amounts of cobalt than true Cobalt spinels of vivid cobalt blue colour.

Absorptivity (a.u.)

Real case at SSEF

400

500

600 Wavelength (nm)

700

800

Spectra from Chauviré et al. 2015 in G&G see also: D’Ippolito et al. 2015 in Physics and Chemistry of Minerals | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 22

| Co-SPINEL vs. BLUE SPINEL A subtle colour change effect may occur in certain spinels containing both, iron and cobalt.

Colour change spinel (84 ct) from Madagascar | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 23

| EMERALD vs GREEN BERYL

Discovered in early 2017, this new find from the Panjshir valley (Afghanistan) has produced a small quantity of emeralds of exceptional quality. | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 24

| EMERALD vs GREEN BERYL

saturation increasing (Cr)

Cr/Fe ratio increasing

strongly Fe dominated

170 ct

230 ct

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 25

| EMERALD vs GREEN BERYL

Christie’s Geneva November 2017 sold for 883’000 US$

Colombian emerald bluish green 9.5 ct

green beryl 230 ct (very low Cr < 0.01 wt%)

Cr-bearing green beryl 180 ct (low Cr, high Fe)

Zambian emerald bluish green 14.5 ct Current Wavelength=602.796 nm

1

Absorbance [A.U]

Absorbance [A.U]

1

0

0

300

350

400

450

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550

600

650

Wavelength [nm]

700

750

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850

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1,000

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Wavelength [nm]

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 26

| EMERALD vs GREEN BERYL Emerald vs Green Beryl (based on chromium and iron ratio)

Tanzania Zambia, Kafubu

10000

Zambia,Musakashi Zimbabwe Russia Pakistan Madagascar

Cr [ppm]

Ethiopia Colombia Brazil Afghanistan

1000

Green Beryl (at SSEF)

100 0.01

0.1

1

10

100

Fe/Cr [ppm]

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 27

| ALEXANDRITE vs CHRYSOBERYL

Alexandrite shows distinct pleochroism, which adds to the complexity of its colour appearance.

Varity defined by presence of colour change effect: Alexandrite is the best known gemstone showing this effect, but a number of other colour changing minerals exist.

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 28

| ALEXANDRITE vs CHRYSOBERYL

Sri Lanka

Sri Lanka

Sri Lanka Russia Russia Hematita, Brazil

LMHC: Colour-change: main hue in daylight differs from that seen in incandescent light. | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 29

| ALEXANDRITE vs CHRYSOBERYL Spectral sensitivity of human S-, M-, and L-cone.

From Moses & Hart 1987.

Chromium absorption spectra in different gems.

Important is the presence of an absorption band at about 570 nm !

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 30

| NOT ALEXANDRITE

Chrysoberyl from Sri Lanka with equal vanadium and chromium concentration. Due to this, the main absorption band is shifted towards a higher wavelength (595 nm), and thus this gemstone shows no colour change effect !

UV-Vis absorption spectra 3.5

Shift of absorption maximum

ν

2

0.851 wt% 0.058 wt% 0.070 wt%

3.0

ν

,

1

2.5

e

Absorbance

Absorbance (a.u.)

EDXRF: Fe2O3 V2O3 Cr2O3

e

574 Kyocera syn.

573 Urals

2.0

576 Hematita 589 M1

1.5

r

595 nm

593 SL4

1.0

599 Tu6 602 SL2 606 Il3

0.5

607 Tu5 0 400

500

600

700

Wavelength (nm)

Figure 14: Non-polarized UV-Vis absorption spectra of V-bearing chrysoberyl from various sources (Il = Ilakaka; Tu = Tunduru; SL = Sri Lanka and M = Mogok), together with Cr-bearing alexandrite from

Schmetzer, Krzemnicki, Hainschwang & Bernhardt, 2013 300

400

500

600

700

800

900

Wavelength (nm)

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 31

| NOT ALEXANDRITE very weak colour shift (no alexandrite!) incandescent

daylight

it=600.00 av=20 s=0 57322 chrysoberyl_0001.abs: 0907135U1- 57322 alexandrite, 600 ms, 20 av., d=7.5 mm

2

alexandrite Absorbance [A.U]

shift of colour (but no alexandrite !)

01: amp=2.7099

1

Fe-chrysoberyl

0

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800

850

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950

Wavelength [nm]

LED light

This Fe-dominated chrysoberyl contains only traces of chromium.

It shows only a colour shift (but no alexandrite colour change effect) due to a nearly monochromatic bluish white LED light source ! | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 32

| CONCLUSIONS For a lab, to distinguish varieties of coloured gemstones requires standardised setup and procedures and (internal) standards (e.g. masterstones or colour charts).

At SSEF variety ID based only on colour -

Ruby vs. Pink Sapphire and Padparadscha vs Pink, Orange, or Fancy Sapphire

At SSEF variety ID based on colour and spectroscopy (chemical composition) -

Cobalt Spinel vs. blue Spinel Emerald vs Green Beryl Alexandrite vs Chrysoberyl

Finally, the result (e.g. ruby or pink sapphire) for is still an expert opinion and may differ from lab to lab in certain cases.

Gemmological laboratories are constantly working together to harmonise their wording (e.g. LMHC) to support the trade and consumers.

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 33

The beauty of gemstones lies beyond their colour and name….

at Inn Chauk, Mogok, Myanmar

| 7 th European Gemmological Symposium EGS | May 2019 | PAGE 34

| THANK YOU FOR YOUR ATTENTION

www.ssef.ch/ssef-facette | 7 th European Gemmological Symposium EGS | May 2019 | PAGE 35