Abstract
The Chinese large freshwater nucleated pearl has become popular for its unique appearance throughout the international jewelry market in recent years. However, its quality evaluation mostly depends on appearance observations, and the influence of the nacre layer’s internal microstructure on the gemstone’s appearance needs further investigation. In this study, light reflectivity, surface height unevenness parameters and porosity of the nacre layer were measured by chroma meter, laser scanning confocal microscope and X-ray computed tomography (μ-CT), which quantitatively described the characteristics of luster, surface roughness and structure compactness of the nacre layer. It was found that the porosity of the nacre layer had a significant influence on appearance features, with an increase of porosity showing more surface blemishes (higher surface roughness parameters) and weaker luster (lower reflectivity). Related results can provide reference for the scientific and quantitative evaluation of pearl quality.
Highlights
A pearl is a variety of gemstone with a unique nacreous luster forming in mussels, consisting mainly of aragonite (CaCO3 ) and minor organic materials.A cultured freshwater nucleated pearl is formed by inserting a selected piece of mantle tissue from a sacrificial mussel, together with a bead nucleus into a partly opened mussel.Currently, about 95% of freshwater pearl production comes from China
Large freshwater nucleated pearls cultured by some Chinese pearl companies have become sought after in the international jewelry market for their amazing size
The luster of pearl samples was measured by chroma meter CS-200 under D65 illuminant and reflected by the surface reflectivity
Summary
A pearl is a variety of gemstone with a unique nacreous luster forming in mussels, consisting mainly of aragonite (CaCO3 ) and minor organic materials (usually under 5%).A cultured freshwater nucleated pearl is formed by inserting a selected piece of mantle tissue from a sacrificial mussel, together with a bead nucleus into a partly opened mussel.Currently, about 95% of freshwater pearl production comes from China. Luster and surface roughness are two important indicators of the grading and evaluation of pearl appearance quality. Regarding the new emerging Chinese large freshwater nucleated pearl, the intrinsic incentives to form different appearance quality characteristics and the influence of internal structure on both the luster and surface roughness deserve to be discussed and analyzed. Previous studies mainly focused on the characteristics and formation mechanism of the microstructure in other different varieties of pearls [1,2,3,4,5,6,7,8,9,10,11,12,13]. The influence of the nacre layer’s porosity on the visual appearance of Chinese large freshwater nucleated pearls, which determines the quality grade, needs deeper investigation
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