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Red Ruby Or Pink Sapphire, That's the Question

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Red Ruby Or Pink Sapphire, That's the Question | 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 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 | 7th 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 | 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 corundum 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 - Gemstone 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 diamonds) or CIE D50 illuminant (at SSEF for coloured gemstones) 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 spectroscopy (& chemistry) using: Master stones or Colour charts (e.g. Munsell, Color 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 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 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 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 > YELLOW -- 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 iron 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 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) Absorbance (a.u.) Absorbance Unstable Colouration of Padparadscha-like 500 600 700 Sapphires Wavelength (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 Thailand 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 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 – | 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
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