Gemmological and Spectral Characteristics of Casque Crafts from Helmeted Hornbil

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.