The Study On Contribution To Yellow Tone Of Natural Citrine From Fe

Citrine is one of the most valuable varieties of crystal, it has been a new favorite among world famous jewelry brands and customers in jewelry market. However, natural citrine is peculiar in nature, the majority is the treatment of amethyst by heating or synthetics, therefore, high-grade natural citrine is very expensive, its quality grading and price appraisal is imminent, and the most important is color grading.Studying the relationship between the color-causing ion Fe and the color parameters, it can not only consummate of the color causing mechanism of citrine, but also guide the practice of color improving and synthetizing, above all, it can supply a set of significative reference data for establishing an objective system of quality evaluation and price appraisal of citrine.In the paper, we get the contents of trace elements in citrine by LA-ICP-MS; afterwards, we use X-rite color i5 spectrophotometer, the external reflected signal of the specimen is firstly adopted by integrating sphere in D65 standard illuminant, and then converted into the parameters in CIEL*a*b* which will realize the quantization of citrine s color on the base of CIE1976L*a*b* uniform color space recommended by CIE. Then we analyze and discuss the correlations among color parameters and the quantitative relationship between the color-causing ion Fe and color parameters with the method of SPSS partial correlation analysis. According to the study, remarkable linear correlation between lightness and hue is obtained when controlling the influence of chroma on lightness, and the correlation coefficient is 0.897 consisting of 4.92% chroma; we also find that the total content of Fe have the closest linear relationship with hue and the correlation coefficient is -0.403, but there has no significant correlation between the total content of Fe and chroma or lightness.Comparing the colors simulated by computer with visual effects, we can find that CIE DE2000 chromatism formula is much more accurate, the results are closer to the chromatism of the specimen by naked eyes, as a result, the formula is more suitable for citrine s chromatism describing, color grading and evaluating; in addition, lightness is the most intuitional representation and fits visual effects better than any other color parameters, consequently, the principal factor to evaluating natural citrine is lightness followed by the integrated contribution of hue and chroma.