Study on the correlation between trace elements and colorimetric parameters of natural blue sapphire

Abstract

Natural blue sapphire is a gem species of corundum, which has high economic value due to its beauty and rarity. Color is the most important factor affecting the price of sapphire and mainly caused by trace elements. However, there is little quantitative data currently available to demonstrate the correlation between trace elements and colorimetric parameters of natural blue sapphire. In this study, the UV‐Vis‐NIR spectra and colorimetric parameters were collected by UV‐Vis‐NIR spectrophotometer while the chemical composition was analyzed by laser‐ablation inductively coupled plasma mass spectrometry. The results show that the content ratio of (FeOT + TiO2)/MgO has negative correlation with b* but positive correlation with Cab*, illustrating its obvious effect on the blue color saturation of natural blue sapphire. In addition, the existence of Cr can produce purple hue and the content of Cr shows positive correlation with hue‐angle hab only in the low range (5‐15 ppm), which implies the content of Cr has a limited influence on the hue of natural blue sapphire and the effect may be more complicated as the content of Cr increases above 15 ppm. This investigation can provide quantitative data for scientific color grading and additional applications of natural blue sapphire.

The Importance of Multidisciplinary Analytical Strategies to Solve Identification and Characterization Challenges in Gemology: The Example of the “Green Stones”

“…on the basis of their characteristic absorption bands. Researchers typically use this information to determine the material's cause of color [74]. Although this technique traditionally requires sample preparation, courtesy of the latest generation of accessories (i.e., integration sphere), the instruments allow the analysis of transparent as well as opaque samples without preparation [75].…”