The New Technology Research Of Gem Color Measuring

Being different from samples of other industries which are complanate and homogeneous, samples of gem have features of small bulk and asymmetric color and diverse carve modal and complicated optics character. Because of these features, it is still depending on the bridle-wise professional in gem industry to distinguish the difference of color and levels of quality by the method of eyeballing and comparison, which is based on the acute power of eyes in resolving tiny difference among colors or standard master stone. But the eyeballing method is usually subjective which leads to uncertainty of color determination in great degree.An automatic detection system of gem color is constructed in this paper in order to give an objective and exact and quantitative description of gem and avoid the impact of lamp-house and environment and subjectivity in color differentiation. In this system, diffuse reflection signals of gem samples are produce by a hemispherical reflector and captured by Fiber-optic combining with spectrum photometer. Information and data is read into the automatic measurement program, and then, the parameters of gem color are quantized. The system is based on the set of principle of color measurement and data and calculating method regards to CIE, i.e. the CIE Standard Colorimetry System.The system runs speedily and steadily with a compact interface and simple operations. During the operation, it has good stability and repetition. The system error, judging by chromaticity data get by the system, is in the error scope permitted with the error of chromaticity coordinate x, y is no great than 0.01(≤0.01), and the error of dominant wavelength is no great than 2% (≤2%). Therefore, it can be used to measure the color parameter of gem quantitatively.The measure system result include all chromaticity system of CIE, from the most original 1931 CIE tristimulus values, chromaticity coordinates to the latest CIE 1976 uniform color space. This convinente the user to chose the need data and keep the data. In addition to the quantity chromaticity data, also show the sample intensity curve, reflectivity curve and the chromaticity diagram in which the chromatic coordinates dots. Especialy, in this procedure replicate the sample color according to tristimulus values, and contrast to the green series of Munsell color system to further the concept of quantity and quality about sample.To take jadeite as an example, make use of this system to get the colorimetry parameter of Jadeite,from which can obtain the rules of Jadeite color discription in quality and quantity. Through the dominant wavelength, we can distinguish the main tone of the jadeite color. According to the chroma, judge the green thick gorgeous degree, and define the quantity concept of the fancy green jadeite. By the contrast of the correlation parameter, we can also judge negative influence of black cover to the jadeite color. By the reflectivity peak value or the difference value of peak and valley, we can tell "good" or "bad" in diaphaneity and texture of Jadeite.The result of experiment illustrated that the gem auto-measurement system is feasible to gem color evaluation and quantity description objectively, with the Fiber-optic spectrum instrument, the appropriate method of lighting and spectrum collection, using the colorimetry principle.