Explaining Colour Change in Pyrope-Spessartine Garnets
A colour-changing garnet exhibits the “alexandrite effect”, whereby its colour changes from green in the presence of daylight to purplish red under incandescent light. This study examines this species of garnets as well as the causes of the colour change by using infrared and ultraviolet visible (UV...
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doaj-a5305e182e7c4d159eb88039636d15972021-08-26T14:06:34ZengMDPI AGMinerals2075-163X2021-08-011186586510.3390/min11080865Explaining Colour Change in Pyrope-Spessartine GarnetsYan Qiu0Ying Guo1School of Gemmology, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Gemmology, China University of Geosciences (Beijing), Beijing 100083, ChinaA colour-changing garnet exhibits the “alexandrite effect”, whereby its colour changes from green in the presence of daylight to purplish red under incandescent light. This study examines this species of garnets as well as the causes of the colour change by using infrared and ultraviolet visible (UV-Vis) spectroscopy. The infrared spectra show that the colour-changing garnets in this paper belong to the solid solution of pyrope-spessartine type. CIE1931 XYZ colour matching functions are used to calculate the colour parameters influencing garnet colour-changing under different light sources. The UV-Vis spectra show two zones of transmittance, in the red region at 650–700 nm and the blue-green region at 460–510 nm. As they exhibit the same capacity to transmit light, the colour of the gem is determined by the external light source. The absorption bands of Cr<sup>3+</sup> and V<sup>3+</sup> at 574 nm in the UV-Vis spectra are the main cause of the change in colour. With the increase in the area of peak absorption, the differences in the chroma and colour of the garnet gradually increase in daylight and incandescent light, and it exhibits a more prominent colour-changing effect.https://www.mdpi.com/2075-163X/11/8/865colour-changing garnetFTIRUV-Vis spectraCIE1931 XYZ colour matching functions |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Yan Qiu Ying Guo |
spellingShingle |
Yan Qiu Ying Guo Explaining Colour Change in Pyrope-Spessartine Garnets Minerals colour-changing garnet FTIR UV-Vis spectra CIE1931 XYZ colour matching functions |
author_facet |
Yan Qiu Ying Guo |
author_sort |
Yan Qiu |
title |
Explaining Colour Change in Pyrope-Spessartine Garnets |
title_short |
Explaining Colour Change in Pyrope-Spessartine Garnets |
title_full |
Explaining Colour Change in Pyrope-Spessartine Garnets |
title_fullStr |
Explaining Colour Change in Pyrope-Spessartine Garnets |
title_full_unstemmed |
Explaining Colour Change in Pyrope-Spessartine Garnets |
title_sort |
explaining colour change in pyrope-spessartine garnets |
publisher |
MDPI AG |
series |
Minerals |
issn |
2075-163X |
publishDate |
2021-08-01 |
description |
A colour-changing garnet exhibits the “alexandrite effect”, whereby its colour changes from green in the presence of daylight to purplish red under incandescent light. This study examines this species of garnets as well as the causes of the colour change by using infrared and ultraviolet visible (UV-Vis) spectroscopy. The infrared spectra show that the colour-changing garnets in this paper belong to the solid solution of pyrope-spessartine type. CIE1931 XYZ colour matching functions are used to calculate the colour parameters influencing garnet colour-changing under different light sources. The UV-Vis spectra show two zones of transmittance, in the red region at 650–700 nm and the blue-green region at 460–510 nm. As they exhibit the same capacity to transmit light, the colour of the gem is determined by the external light source. The absorption bands of Cr<sup>3+</sup> and V<sup>3+</sup> at 574 nm in the UV-Vis spectra are the main cause of the change in colour. With the increase in the area of peak absorption, the differences in the chroma and colour of the garnet gradually increase in daylight and incandescent light, and it exhibits a more prominent colour-changing effect. |
topic |
colour-changing garnet FTIR UV-Vis spectra CIE1931 XYZ colour matching functions |
url |
https://www.mdpi.com/2075-163X/11/8/865 |
work_keys_str_mv |
AT yanqiu explainingcolourchangeinpyropespessartinegarnets AT yingguo explainingcolourchangeinpyropespessartinegarnets |
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