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| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 2
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 3
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 4
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 5
| 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 6
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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 7
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…)
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 8
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 9
| 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 10
| RUBY vs 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)
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 11
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 12
| 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 13
| 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 14
| 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*)
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 15
| NOT PADPARADSCHA
Colour modifier:
Pink sapphire containing orange iron hydroxide. Although visually orangey pink this stone does not qualify for padparadscha.
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 16
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 17
| 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)
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 18
| Co-SPINEL vs. BLUE SPINEL
Where is the limit ?
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 19
| 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
Roman Co-coloured perfume bottle. © scottishantiques.com
Co-treated corundum. © GIT Thailand
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 20
| Co-SPINEL vs. BLUE SPINEL
Co-diffusion treatment of low quality spinel
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 21
Spectra from: Hanser C. 2013 (unpublished Bachelor thesis, University Freiburg i. Br. (Germany) in collaboration with SSEF
| 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 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 22
400
Wavelength (nm)
Ab
so
rpti
vit
y (
a.u
.)
500 600 700 800
| 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.
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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 23
| Co-SPINEL vs. BLUE SPINEL
Colour change spinel (84 ct) from Madagascar
A subtle colour change effect may occur in certain spinels containing both, iron and cobalt.
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 24
| 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.
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 25
| EMERALD vs GREEN BERYL
satu
rati
on
in
cre
asi
ng
(C
r)Cr/Fe ratio increasing
230 ct170 ct
strongly Fe dominated
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 26
| EMERALD vs GREEN BERYL
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$
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 27
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)
| EMERALD vs GREEN BERYL
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 28
| 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.
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 29
| ALEXANDRITE vs CHRYSOBERYL
LMHC: Colour-change: main hue in daylight differs from that seen in incandescent light.Hematita, Brazil
Russia
Russia
Sri Lanka
Sri Lanka
Sri Lanka
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 30
| ALEXANDRITE vs CHRYSOBERYL
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.
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 31
| 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%
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 32
| 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
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 33
| 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 34
The beauty of gemstones lies beyond their colour and name….
at Inn Chauk, Mogok, Myanmar
| 7th European Gemmological Symposium EGS | May 2019 | PAGE 35
| THANK YOU FOR YOUR ATTENTION
www.ssef.ch/ssef-facette
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