Impact of different standard lighting sources on red jadeite and color quality grading

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. ABSTRACTImpact of different standard lighting sources on red jadeite and color quality grading Impacto por diferentes fuentes de iluminación estándar en la clasificación de jadeíta roja y la calidad del color

The Effect of Munsell Neutral Value Scale on the Color of Yellow Jadeite and Comparison between AP and K-Means Clustering Color Grading Schemes

“…Due to the transparency and characteristic absorption of the yellow jadeite, the testing backgrounds and light source would make a significant influence on the color. In our previous study, we have discussed the impact of the different light sources on jadeite and concluded that the standard D65 light source is suitable for color grading compared with A and CWF [8]. So, in this paper, the Munsell neutral value scales (N0.5, N1, N1.5, N2, N2.5, N3, N3.5, N4, N4.5, N5, N5.5, N6, N6.5, N7, N7.5, N8, N8.5, N9, N9.5) were used as the backgrounds for 33 yellow jadeite color measurements.…”

“…Depending on the degree of weathering received, the secondary color of jadeite shows continuous changes. The least weathered part is grayish-green, and its color-causing mineral is thought to be chlorite, while yellow and red jadeite receive a higher degree of weathering, the main crack filler is limonite colloid (hematite, goethite), and the most intense weathering of the surface layer showing black [7,8].…”

The Objective Conditions Study and Optimization of Digital Imaging System on Color Measurement：Case with Jadeite

“…These methods are mainly based on the subjective evaluation of the color by the operator, so it takes a lot of time and money to train professional graders. UV-Vis spectrophotometers can provide accurate absorption spectra from which color calculations can be made 2,3 ; however, the complex conversion process has hindered their development in gemstone color measurement; hand-held spectrophotometers, as the mainstream gem color measurement tool at present, has been used to measure the color of jadeite green 4 , jadeite red 5,6 , turquoise 7 , peridot 8,9 , amethyst 10 , chrysoprase 11,12 , and extensive gemstone chromatography studies. Because of its convenient operation and reliable data, this tool has already been favored by researchers.…”

“…The cause of the color of jadeite can be divided into two types: primary color and secondary color 6,28 ; The green of jadeite is the primary color; and the red and yellow is the secondary color, which is caused by exogenous geological activities, and usually produced when impurities, such as water-containing iron oxide, are infiltrated along the cracks and the grain boundaries that are not tightly bound. According to comparative experiments, Wang et al recognized that the D65 standard light source (representing the average daylight with a color temperature of 6504K) is the most suitable light source for evaluating Jadeite green 29 ; Pan et al, Guo, Li believe that D65 light source is suitable to evaluate the red color of jadeite, tourmaline, and ruby respectively 6,30,31 . The color of jadeite is the most important indicator of value, so it is important to accurately measure and display its color.…”

The impact of trace metal cations and absorbed water on colour transition of turquoise

“…Serving as the foundation for the quantitative characterization of colour, this colour system possesses good colour uniformity, where the colour difference observed by the naked eye is positively correlated with that calculated by colorimetric coordinates in this system [39,40]. The colour system is widely applied in the study of gem's colour, including jadeite-jade [41][42][43], peridot [44,45], tourmaline [46], amethyst [47] and diamond [48]. The formula CIE DE2000 can be used to express colour difference quantitatively and effectively [49][50][51].…”