Abstract

The purpose of this paper is to investigate the standard light source for grading and displaying the color of red jadeite and to classify the color. With Raman spectrometer, ultraviolet-visible spectrophotometer and X-ray fluorescence spectrometer, the results show that, the Fe 3+ is the main chromogenic mineral of red jadeite, which negatively correlates with the tonal angle, while the color of red jadeite has a positive correlation with the hematite content. The color of 120 red jadeite samples was examined by collecting the reflective signaled from the sample surface using an integrating sphere with the portable X-Rite SP62 spectrophotometer based on CIE 1976 L*a*b* uniform color space. The color parameters of jadeite samples under D65, A and CWF standard light sources were analyzed. The light spectrum of D65 light source is continuous, relatively smoothed with high color temperature, which makes the sample color close to that under the natural light and can be used as the best evaluation light source. A light source contributes to improve the red tone of jadeite, which is the best light source for commercial display of red jadeite. CWF light source can be used as the auxiliary lighting for color evaluation. The color of red jadeite is divided into five levels from best to worst using K-Means cluster analysis and Fisher discriminant analysis under D65 light source: Fancy Vivid, Fancy Deep, Fancy Intense, Fancy dark and Fancy.

Highlights

  • Jadeite is generally considered to be a high-pressure mineral (Yang, Yang & Long, 2015), which is called the “King of Jade” in China

  • D65 light source is suitable for the jadeite evaluation, A light source is suitable for exhibiting the red color of jadeite, which can be used to sale and display jadeite

  • Conclusions were given based on comprehensive analysis: (1) Fe 3+ is the main chromogenic mineral of red jadeite

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Summary

Introduction

Jadeite is generally considered to be a high-pressure mineral (Yang, Yang & Long, 2015), which is called the “King of Jade” in China It generally occurs as block, and is a rare rock type formed in subduction zones with two origins: the wholesale metasomatic replacement and the vein precipitation (Yui & Fukuyama, 2015; Mevel & Kiénast, 1986). Jadeite is a fibrous mineral aggregate composed of pyroxene minerals with jadeite and omphacite as the main minerals. It typically has different percentages of diopside (CaMgSi2O6)/ kosmochlor (NaCrSi2O6 ), iron-rich pyroxene (CaFe2 + Si2O6 ) and aegirine (NaFe3 + Si2O6 ), which coexist with jadeite as solid solutions (Harlow & Olds, 1987). The composition of jadeite varies with place of origin, e.g., jadeite from the Burma contains soda amphibole (including ekman rutile, blue amphibole, sodium tremolite and amphibole), albite, zeolite, tremolite, rutile, clinochlore, barium albite and chromite, etc (Htein & Naing, 1994, 1995)

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