Quick viewing(Text Mode)

Red Ruby Or Pink Sapphire, That's the Question

Red Ruby Or Pink Sapphire, That's the Question

| or Pink , that’s the Question Where 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

| 7th European Gemmological Symposium EGS | 2019 | PAGE 1 | CONTENTS

1) Introduction:

Creation of standards and standardised procedures

2) Real cases at SSEF:

- Ruby vs Pink Sapphire - Padparadscha vs Fancy - vs Spinel - vs - Alexandrite vs

3) Conclusions

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 2 | TERMS & SIGNIFICANCE

Mineral: - Scientifically well defined term !

- CNMMN (Commission on New and 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 to polycrystalline aggregates ( – 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

| 7th 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, The wheel of colour of natural LMHC,...).

Gemmological laboratories are constantly working together to further harmonise their wording.

see for example LMHC infosheets: www.lmhc-gemmology.org

| 7th 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.

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

Light source:

- Colour observation from the top

- slightly tilted 10-20° in all directions Spectral distribution of D50 illuminant, - Standardised light (ideally continuum, e.g. compared to halogen and fluorescent light. filtered halogen or LED lamp equivalent to CIE D65 (at SSEF for ) or CIE D50 illuminant (at SSEF for coloured ) and with high colour rendering efficiency.

Comparison of CIE D65 and CIE D50

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 6 | OPTIONS TO DISTINGUISH GEMSTONE VARIETIES based on: Colour only or Colour and (& chemistry) using: Master stones or Colour charts (e.g. Munsell, CodexTM…)

| 7th 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 ruby Pinkish red ruby Purplish red ruby

Pink pink sapphire purple sapphire

| 7th 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

| 7th 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

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 10 | RUBY vs PINK SAPPHIRE

Zoning vs visual appearance

There is no specific 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

| 7th 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.

| 7th 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)

| 7th 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

10

5 > --

b* 0 -- BLUE < -5

-10

-15

-20 -20 -15 -10 -5 0 5 10 15 20 GREEN <-- a* --> RED

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 14 | NOT PADPARADSCHA

Colour modifier:

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

| 7th 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

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 16 | NOT PADPARADSCHA: UNSTABLE COLOUR

slight to moderate colour shift FEATURE ARTICLE (still padparadscha)

Figure 1: This 9.1 ct sapphire from the Ambatondrazaka area of 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) Absorbance (a.u.) Absorbance

Unstable Colouration of Padparadscha-like 500 600 700 Sapphires (nm) Michael S. Krzemnicki, Alexander Klumb and Judith Braun

ABSTRACT: After the October 2016 discovery of a new gem deposit at Bemainty near Ambaton- drazaka, Madagascar, a number of sapphires with padparadscha-like colour entered the trade. Further reading: 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 origi- nating from Madagascar (Ambatondrazaka and Ilakaka) and Sri Lanka. The 48 samples could be Journal of Gemmology (Gem-A) 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 and InColor 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 and SSEF Facette 24, 2018 proper gemmological identification of any sapphire showing a yellow to orange colour component.

The Journal of Gemmology, 36(4), 2018, pp. 346–354, http://doi.org/10.15506/JoG.2018.36.4.346 https://www.ssef.ch/ssef-facette/ © 2018 The Gemmological Association of Great Britain and new LMHC website (Infosheet 4) 346 THE JOURNAL OF GEMMOLOGY, 36(4), 2018 https://www.lmhc-gemmology.org/gemstones

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 17 | Co-SPINEL vs. BLUE SPINEL

Where is the limit ?

| 7th 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 Roman Co-coloured perfume bottle. © scottishantiques.com

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 19 | Co-SPINEL vs. BLUE SPINEL

Co-diffusion treatment of low quality spinel

| 7th 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 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. () in collaboration with SSEF – | 7th 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 colour.

Real case at SSEF Absorptivity (a.u.)

400 500 600 700 800 Wavelength (nm) Spectra from Chauviré et al. 2015 in G&G see also: D’Ippolito et al. 2015 in Physics and Chemistry of Minerals

| 7th 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

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 23 | EMERALD vs GREEN BERYL

Discovered in early 2017, this new find from the Panjshir valley () has produced a small quantity of of exceptional quality.

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 24 | EMERALD vs GREEN BERYL

Cr/Fe ratio increasing strongly Fe dominated )

r 170 ct 230 ct C (

g in s a e r c in

on i t a r u t sa

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 25 | EMERALD vs GREEN BERYL

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

Colombian emerald Zambian emerald Cr-bearing green beryl green beryl bluish green bluish green 180 ct 230 ct 9.5 ct 14.5 ct (low Cr, high Fe) (very low Cr < 0.01 wt%)

Current Wavelength=602.796 nm

1

1 A.U] A.U] [ [ Absorbance Absorbance

0

0

300 350 400 450 500 550 600 650 700 750 800 850 900 400 500 600 700 800 900 1,000 300 400 500 600 700 800 900 1000 300 400 500 600 700 800 900 1000 Wavelength [nm] Wavelength [nm]

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 26 | EMERALD vs GREEN BERYL

Emerald vs Green Beryl (based on chromium and iron ratio)

Tanzania

10000 , Kafubu Zambia,Musakashi

Zimbabwe

Russia

Pakistan

Madagascar

Ethiopia

Colombia

Brazil Cr [ppm] 1000 Afghanistan Green Beryl (at SSEF)

100 0.01 0.1 1 10 100 Fe/Cr [ppm]

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 27 | ALEXANDRITE vs CHRYSOBERYL

Alexandrite shows distinct , 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.

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 28 | ALEXANDRITE vs CHRYSOBERYL

Sri Lanka

Sri Lanka

Sri Lanka

Russia

Russia LMHC: Colour-change: main in daylight differs from Hematita, that seen in incandescent light.

| 7th 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 !

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 30 | NOT ALEXANDRITE

Chrysoberyl from Sri Lanka with equal 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

e 3.5 EDXRF: ν Shift of absorption 2 maximum Fe2O3 0.851 wt% 3.0 , ν V2O3 0.058 wt% 1 2.5 Cr2O3 0.070 wt% 574 Kyocera syn.

573 Urals 2.0 e 576 Hematita

1.5 Absorbance 589 M1 r 593 SL4 595 nm 1.0

Absorbance (a.u.) Absorbance 599 Tu6 602 SL2 0.5 606 Il3 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 Schmetzer= Ilakaka; Tu = Tunduru;, Krzemnicki SL = Sri Lanka and, MHainschwang = ), together with Cr-bearing& Bernhardt, alexandrite from 2013 300 400 500 600 700 800 900 Wavelength (nm)

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 31 | NOT ALEXANDRITE

very weak colour shift (no alexandrite!)

01: amp=2.7099 it=600.00 av=20 s=0 57322 chrysoberyl_0001.abs: 0907135U1- 57322 alexandrite, 600 ms, 20 av., d=7.5 mm incandescent daylight 2 alexandrite

1 Absorbance[A.U]

0 Fe-chrysoberyl

400 450 500 550 600 650 700 750 800 850 900 950 Wavelength [nm] LED light shift of colour (but no alexandrite !) alexandrite no (but colour of shift

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 !

| 7th 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.

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 33 The beauty of gemstones lies beyond their colour and name….

at Inn Chauk, Mogok,

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 34 | THANK YOU FOR YOUR ATTENTION

www.ssef.ch/ssef-facette

| 7th European Gemmological Symposium EGS | May 2019 | PAGE 35

Top View