Gemmological and Spectral Characteristics of Casque Crafts from Helmeted Hornbil
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摘要: 对市场上出现的盔犀鸟头胄工艺品及其拼合制品、仿制品，在宝石显微镜下放大观察，采用扫描电子显微镜、傅里叶变换红外光谱仪、紫外－可见光谱仪、激光拉曼光谱仪等大型分析仪器进行测试，探究其物质组成、生长结构、颜色成因以及鉴定方法。结果表明，盔犀鸟头胄整体表现为层状鳞片生长结构，头胄工艺品的黄色基体中普遍发育近平行条带生长结构，红色圆斑与黄色基体呈渐变过渡关系；红外光谱表现为酰胺特征吸收谱带，表明角蛋白为头胄主要成分；特征的紫外－可见吸收光谱与拉曼光谱均标志着类胡萝卜素的存在，且类胡萝卜素是头胄的主要呈色原因。拼合工艺品的红色圆斑具有清晰边界并可见拼合缝隙，红外光谱显示红色圆斑为人造树脂材料。仿制品的黄色基体内部可见气泡，红外光谱揭示其整体均为人造树脂。Abstract: Helmeted Hornbill(Rhinoplax vigil),a kind of large hornbill,whose unique solid cutin casque is usually used for carving and crafting,ranges across regions of Southeast A-sia and is presently being near threatened.In this paper,in order to investigate the material composition,growth structure,colour genesis and identification method,the structure along with characteristic vibrational spectra and ultraviolet-visible spectra of casque crafts from Helmeted Hornbill,as well as the composites and imitations,which appear on the market,are investigated with the help of gem microscope,scanning electron microscope,Fourier transform infrared spectrometer,ultraviolet-visible spectrometer and laser Raman spectrometer.Observation and testing results show that the Helmeted Hornbill casque develops a layered-scale structure.Scales,sized between 30-50 μm,are constructed of organic matter in rodlike or granular shapes.Subparallel stripe growth structures are commonly seen on the yellow matrix of casque crafts,meanwhile a gradual change of colour exists between the yellow matrix and the red round spot.Infrared absorption spectra of the casque crafts present the characteristics of peptide bond,comprising Amide I band at 1 648cm-1 caused by ν(C-O)stretching vibration,AmideⅡband at 1 540cm-1 caused by δ(N-H)bending vibration,AmideⅢband at 1 242cm-1 caused by ν(C-N)stretching vibration and Amide A broad band at 3 280cm-1 caused by ν(N-H)stretching vibration,indicating that the casque is mainly composed of keratin.Raman peaks at 1 517and 1 153cm-1 are resulted from ν(═C C)and ν(C-C)stretching vibrations of polyprene skeleton,indicating the existence of carotenoids.In addition,diversity between Raman intensities on different sections of the casque suggests a higher carotenoid content in the red section.UV-Vis absorption bands at 431,457and 486nm are attributed to conjugated double bonds in olefin chain of carotenoid,which absorbs the blue-violet region of the visible light and results in the colours of the casque.Otherwise,as for the composites,the yellow matrix is made of Helmeted Hornbill cutin casque as well,but the red round spot is a pasted slice,whose infrared spectrum shows the characteristic spectrum of acrylate resin.The edge of the pasted slice presents a clear borderline,meanwhile a distinct slit can be observed under top lighting.As for the imitations,whose infrared spectrum shows the characteristic spectrum of unsaturated polyester resin,no subparallel stripes growth structure appears on the yellow matrix,however round bubbles are observed inside the matrix.Infrared absorption band at 1 731cm-1 caused by ν(C-O)stretching vibration is owned by both the composited slices and imitations,indicating their resin component.
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