便携式高光谱感应器在有机胶料无损分析中的应用初探

Preliminary Study on the Non-Invasive Characterization of Organic Binding Media Employing a Portable Hyperspectral Sensor

文物和艺术品的无损分析是文化遗产科技保护的重点和难点。该研究使用了一种遥感领域的地物光谱仪——便携式全波段高光谱感应器(Analytical Spectral Devices FieldSpec FR Pro 3)分析文物中常用的有机胶料。这种高光谱感应器可以在0.2 s内获得一个350~2500 nm全波段反射光谱,其波段涵盖了可见光、近红外和短波红外三个区域。该研究选取蛋黄、兔皮胶、亚麻籽油三种中西方古代、现代常用的胶结物作为研究对象,分别以单组分、与不同颜料的混合物两种形式来验证该设备无损分析的可靠性和实用性。首先按照传统绘画技法,使用四种不同颜料与上述胶结物的组合制备彩绘样品。待样品完全干燥后,使用探头直接接触法获取光谱信息,并利用相关软件进行数据处理。实验发现,由于物化本质不同,这三种胶结物的反射光谱在波长1100~2400 nm范围内的特征信息差异最为显著。当胶料与无机颜料混合后,这三种有机物的吸收峰位置相对于单组分出现了相同的三种变化:(1)波长1507 nm处的肩峰消失;(2)波长约为1943~1922 nm处的宽峰偏移;(3)位于波长2050 nm处的原N—H伸展和弯曲合频峰向右移动了约(20~2070 nm)。值得注意的是,C—H合频和倍频峰在单组分与混合物光谱中的位置保持一致。这一系列谱图变化规律使得从混合物中鉴别胶料具有了可能性。尽管在某些情况下,和其他光谱分析技术类似,混合后无机颜料和有机胶料吸收峰之间的相互干扰会影响胶料的鉴定,但利用其一阶导数光谱能够协助各组分的准确表征。结果表明,该高光谱感应器能够有效鉴别有机胶料;这种快速、无损的分析方法不仅在实验室成分分析中具有可行性,而且其便携的特点也适用于文物保护与修复现场的快速分析,具有较好的实用性。

Non-invasive analysis of artworks is one of the essential requirements in heritage conservation.In this study,a spectroradiometer in the field of remote sensing-a portable,full range hyperspectral sensor—was used to characterize organic compounds commonly found in cultural relics.It can obtain a continuous reflection spectrum within 0.2 s in the range of 350~2500 nm,which covers visible,near-infrared and short-wave infrared regions.In the study,the three most widely used binders(egg yolk,rabbit skin glue,and linseed oil)were analysed.Four different pigments were used to mix with them to prepare painting mock-ups.This technique’s applicability and accuracy were verified by testing a single component and a mixture of binders with pigments.The most diagnostic information of the three binders mainly lies in the range from 1100 to 2400 nm.Once the binders were mixed with inorganic pigments,the original position of the peaks experienced three types of modifications:(1)the shoulder peak at about 1507 nm disappeared;(2)the broad peak between 1943~1922 nm shifted;(3)the absorption peak of N—H stretching and bending combination band at 2050 nm shifted to about 2070 nm.It is worth noting that the absorption peaks of the C—H combination and overtone bands showed the same positions in the spectra of single component and mixtures.Although in some cases,the interference between the absorption peaks of inorganic pigments and organic compounds influence on the identification,the use of their first derivative transformation can ameliorate this situation.Results showed that the hyperspectral sensor could effectively identify organic binders.This fast and non-destructive technique is feasible not only in laboratory conditions,but its portability also allows for in-situ analyses in outdoor environments.