Study On Color Characteristics And Dyeing Experiments Of Pinctada Martensii Pearls

Pinctada martensii is the main cultured seawater pearl shell in China, and Guangxiprovince is also one of the main origin of seawater cultured pearls of pinctada martensii.This kind of pearls are loved by people with their pretty luster and their mellow, full andgreat.This paper, had collected the pearl samples of pinctada martensii from BeihaiGuangxi Province. Color varies from white, cream to golden yellow. Some research alsohas been done on surface features, spectral features and composition of the traceelements to discuss color characteristics of these samples through using some moderntesting methods such as UV-Lamp, FTIR, Raman, UV-NIS and ICP-MS. Two commonchemical dyes were used to dye some cream color samples.Research on the surface features of seawater cultured pearls from Beihai GuangxiProvince show that these samples have uniform golden yellow color, gentle luster andsmooth surface. Imbricate structure of the surface is clearly visible. Under long waveultraviolet fluorescence, golden yellow samples have a typical yellow-greenfluorescence characteristics, cream and white pearls have a typical-strong bluefluorescence, short-wave ultraviolet fluorescence of these samples were not obvious.Typical aragonite and water spectrum were characterized by infrared spectroscopy.But the results showed that pearls of different color have no significant differences onthe absorption peak.Aragonite and anionic CO₃^2-Raman spectrum peaks were visible. Raman peak of thewater is less obvious and suggests little differences between samples of various kinds.The stable typical aragonite peaks are observed for the golden seawater pearls with lessimpurity peak burr. Golden yellow seawater pearls have an obvious Raman shift causedby aragonite crystal lattice near the275cm^-1.Golden seawater pearls have the typical UV-NIS characteristics of biggest wideabsorption band of356nm-centered, and show selective absorptions of various intensityfrom400⁵00nm. Due to the low color saturation, absorption intensity at356nm isrelatively low. Two apparent ultraviolet absorption peaks-284nm and356nm in therange of200⁴00nm-can also be observed in UV-NIS absorption spectrum.Analysis of trace element content of these seawater pearls suggests that the content ofNa, Mg, K and Sr are higher than that of Ag, Mn, Ba and Pb.Some cream seawater pearls were being dyed to discuss and compare the bestcondition of dyeing and the pearls being dyed by two kinds of chemical dyes which areharmless and cheap. Pearls can be dyed into golden yellow color by these two chemicaldyes, but the same as all surface dyeing these pearls have drawbacks-concentration ofdye around pearl orificen and uneven color under the microscope.