Study On Spectral Characteristics And Color Attributes Of Copal From Madagascar And Borneo

Copal is a kind of natural organic compounds containing C, H, O, S, N elements, which is formed by the resin with complex geological processes and fossilization. Due to the shorter burial time, the maturity of copal is less than amber. Using the copal from Madagascar and Borneo and amber from Burma and Baltic as research objects, the paper has been done some researchs on gemological and spectral characteristics mainly through using modern testing methods such as microscope and analysis of Infrared Spectroscopy, Raman Spectroscopy and Color i5 spectrophotometer based on CIE 1976 L*a*b* uniform color space, The purpose is to analyze the types and characteristics of functional groups in copal, and to find the differences between copal and amber from different localities, which can provide a scientific basis for the study of copal.128 pieces of brownish red Borneo copal and 54 pieces of yellow Madagascar copal were measured under standard illuminant D65 and standard illuminant A by Color i5 spectrophotometer based on CIE 1976 L*a*b* uniform color space. The data shows that, the Borneo copal samples mainly concentrate on the central of red zone and yellow zone of chromaticity diagram, partial samples are on the blue zone; Madagascar copal samples concentrate on the central of yellow zone. The lightness value(L*)of Borneo copal is lower than Madagascar copal, the lightness value of Madagascar copal is in the medium range, and the lightness value of most Borneo copal is in the low range. Chroma range of Borneo copal samples is smaller and the value of chroma is lower than Madagascar Copal.Due to the different shades of specimens, the color of copal samples is largely affected by the lightness of background. Color i5 spectrophotometer is used to measure the change of lightness of 64 pieces of brownish red Borneo copal samples and 54 pieces of Madagascar copal samples, with 5 kinds of Munsell Neutral Value Scale, the lightness value of which are 2, 22, 43, 63, 84, used as the background of copal samples. The Munsell Neutral Value Scale used as background has greater effects on yellow Madagascar copal with high transparency than brownish red translucent Borneo copal. At the same time, data shows that the higher lightness copal has, the more vulnerable samples will be.