| Red Ruby or Pink Sapphire, that’s the Question · | 7th European Gemmological Symposium EGS | May 2019 | PAGE 6 Light source: - Colour observation from the top - Gemstone slightly

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

| Red Ruby or Pink Sapphire, 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


| 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


| TERMS & SIGNIFICANCE

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.

Mineral:- Scientifically well defined term !

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

Beryl colour varieties


| 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,...).

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

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

The wheel of colour of natural corundum


| 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.


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.

| STANDARDISED PROCEDURES

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

Comparison of CIE D65 and CIE D50


based on:

Colour only or Colour and spectroscopy (& chemistry)

| OPTIONS TO DISTINGUISH GEMSTONE VARIETIES

using:

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


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

At SSEF, we differentiate:

Red rubyPinkish red rubyPurplish red ruby

Pink pink sapphirePurple purple sapphire


| 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



ruby 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)



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


| PADPARADSCHA

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


| 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)


| PADPARADSCHA

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

-20

-15

-10

-5

0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 20

BLU

E<--b*-->YELLOW

GREEN<-- a*-->RED

GCATransmissionAVERAGEDColor(a*,b*)


| NOT PADPARADSCHA

Colour modifier:

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


| NOT PADPARADSCHA: UNSTABLE COLOUR

This pink sapphire was submitted to us as a ‘padparadscha’ !

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…

…so this fancy sapphire is pink again after few weeks exposure to daylight


| NOT PADPARADSCHA: UNSTABLE COLOUR

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/gemstones346 THE JOURNAL OF GEMMOLOGY, 36(4), 2018

FEATURE ARTICLE

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 Ambaton-

drazaka, 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 origi-

nating 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.

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

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.

500 600 700

Wavelength (nm)

Ab

sorb

an

ce (

a.u

.)

slight to moderate colour shift

(still padparadscha)

distinct to strong colour shift

(not padparadscha)


| Co-SPINEL vs. BLUE SPINEL

Where is the limit ?



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

Roman Co-coloured perfume bottle. © scottishantiques.com

Co-treated corundum. © GIT Thailand



Co-diffusion treatment of low quality spinel


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


UV-Vis absorption spectroscopy

Co2+ and Fe2+ both may produce a blue colour in spinel. Using classic ED-XRF analysis, cobalt is in most spinelsbelow 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


400

Wavelength (nm)

Ab

so

rpti

vit

y (

a.u

.)

500 600 700 800


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.

see also: D’Ippolito et al. 2015 in Physics and Chemistry of Minerals

Spectra from Chauviré et al. 2015 in G&G

Real case at SSEF



Colour change spinel (84 ct) from Madagascar

A subtle colour change effect may occur in certain spinels containing both, iron and cobalt.


| 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.



satu

rati

on

in

cre

asi

ng

(C

r)Cr/Fe ratio increasing

230 ct170 ct

strongly Fe dominated



Wavelength [nm]900850800750700650600550500450400350300

Ab

so

rba

nce

[A

.U]

1

0

Colombian emerald

bluish green9.5 ct

Current Wavelength=602.796 nm

Wavelength [nm]1,000900800700600500400

Ab

so

rba

nce

[A

.U]

1

0

1000900800700600500400300

Zambian emerald

bluish green14.5 ct

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

1000900800700600500400300

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

Christie’s Geneva November 2017

sold for 883’000 US$


100

1000

10000

0.01 0.1 1 10 100

Cr[ppm]

Fe/Cr[ppm]

EmeraldvsGreenBeryl(basedonchromiumandironratio)

Tanzania

Zambia,Kafubu

Zambia,Musakashi

Zimbabwe

Russia

Pakistan

Madagascar

Ethiopia

Colombia

Brazil

Afghanistan

GreenBeryl(atSSEF)



| ALEXANDRITE vs CHRYSOBERYL

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.

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



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

Russia

Russia

Sri Lanka

Sri Lanka

Sri Lanka



Chromium absorption spectra in different gems.

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

Spectral sensitivity of human S-, M-, and L-cone. From Moses & Hart 1987.


| 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 !

Schmetzer, Krzemnicki, Hainschwang & Bernhardt, 2013

e

,

e

r

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

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Ab

sorb

an

ce

UV-Vis absorption spectra

574 Kyocera syn.

Shift of absorption

maximum

400 500 600 700Wavelength (nm)

607 Tu5

606 Il3

602 SL2599 Tu6

593 SL4

589 M1

576 Hematita

573 Urals

ν2

ν1

Ab

sorb

an

ce (

a.u

.)

Wavelength (nm)

300 400 500 600 700 800 900

595 nm

EDXRF:Fe2O3 0.851 wt%V2O3 0.058 wt%Cr2O3 0.070 wt%


| NOT ALEXANDRITE

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 !

very weak colour shift (no alexandrite!)sh

ift

of

co

lou

r (b

ut

no

ale

xa

nd

rite

!) daylightincandescent

LED light

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

Wavelength [nm]950900850800750700650600550500450400

Ab

so

rba

nce

[A

.U]

2

1

0

alexandrite

Fe-chrysoberyl


| 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.


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

at Inn Chauk, Mogok, Myanmar


| THANK YOU FOR YOUR ATTENTION

www.ssef.ch/ssef-facette

Documents

| Red Ruby or Pink Sapphire, that’s the Question · | 7th European Gemmological Symposium EGS | May 2019 | PAGE 6 Light source: - Colour observation from the top - Gemstone slightly