Study On Mechanism Of Seawater Pearl Dyeing And Optimization Of Dyeing Technology

Pearl, of which the value was mainly determined by luster and color, is a valuable kind of organic gem. In order to ensure the color of pearl uniformity and meet favorite color of different people, pearl dyeing were used as an important method to process the cultured pearl. Differences still could be seen between nature color pearls and the pearls dyed by the existing processing technology, and which component of pearl combined with dye was not clear. To discuss about the mechanism of sea-water pearls dyeing, in this study, through a variety of testing means, we researched the penetration ways of dye liquor in the dyeing process of sea-water pearls, analyzed the physical and chemical properties changes of pearls before and after dyeing, and optimized the existing dyeing process of seawater pearls.In this work, we research on the changes of configuration of surface and cross section, ion species and their content, organic and inorganic mineral phases in the pearls before and after dyeing by scanning electron microscopy(SEM),Gemological microscope, Microscopic spectrophotometer-polarizing microscope, Inductively coupled plasma mass spectrometry(ICP-MS), Fourier transform infrared spectroscopy(FTIR)and Micro-Raman spectroscopy(Micro-Raman).The microscopic observation results were as follows:1, in the dyeing process, the dyes penetrated into the interior of pearls mainly through the loose organic parts of the pearl surface, the gap between the bead nucleus and the nacreous layers. 2, the phenomenon of dye enrichment, which could be removed by fade processing, appeared in the damaged or defective surface of poor quality pearls after dyeing.3, the brick-and-mortar structure of the pearl were not changed after dyeing. Phase analysis showed that the dyes connected with the organic matter of the pearl. As the element analysis results showed, the level of Cu and Mg Ions significantly decreased while Fe, Ba and Zn Ions increased in the dyeing process. As the gloss analysis showed, dye molecules combined with the organic matter between the crystal layers of pearl surface, through which the molecular gap caused by bleaching could be filled, the mirror effectiveness of pearl surface would be enhanced and pearl surface gloss were improved after dyeing. Therefore, the mechanism of pearl dyeing were that the dye molecules could be combined with a particular group (-NH or-OH) from the organic matter of pearl through chemistry or adsorption effect.Based on the Local standards in Guangdong Province <Pearl Staining Norms>, the dyeing process of sea-water cultured pearls were improved. Mono-factor tests were undertaken to screen dyeing solvent, pH, and dosage of surface active agents (SAA). After the best level of the three factors was determined, the effects of the three main factors (dye concentration, dyeing temperature and dyeing time) on the dyeing results were obtained by the means of orthogonal experiment analysis. The results were as follows: in the dyeing process of sea-water pearls, effect of dye temperature on dyeing results were the greatest, and the effect level of dye concentration and dye time on dyeing results of different dyes were unlike, the best level of the three factors was also identified.