光纤反射光谱法（FORS）

达妮埃拉·平娜（Daniela Pinna）

1．分类

光纤反射光谱法（fibre optic reflectance spectroscopy，FORS）是一种非侵入式检测技术。用于FORS分析的分光光度计可测量光谱的紫外段、可见光段和近红外段。

2．说明

分光光度计测量的是一种材料对一个谱段的光的反射比，测量结果以光谱曲线的形式给出，可反映材料反射的能量与波长（单位：nm）的关系。FORS用的是便携式分光光度计，配有光纤，可采集对象表面的反射光谱。大部分绘画材料都具有特定的光谱特征，采集UV-VIS-NIR谱段内的光谱，就可以得出它们在VIS-NIR谱段的综合指标（图1）。

图1 青金石和蓝铜矿的反射光谱［感谢苏珊娜·布拉奇（Susanna Bracci）］

3．应用

FORS已应用于绘画和彩绘表面的颜料与染料鉴定。作为一种非侵入性技术，FORS可以对物体表面的不同区域进行广泛的光谱表征，加上低成本小型光谱仪的普及，它已成为一种常用的强大原位检测技术。

4．局限性

反射光谱法对材料的鉴定能力在很大程度上取决于获取到的光谱品质（光谱分辨率），以及是否拥有可靠的标准谱谱库。当存在复杂混合物时，FORS无法得出准确的结果。此外，有些反射光谱相似的颜料（如镉红和朱砂）也无法用FORS来区分。

5．补充技术

紫外照相术、X射线荧光光谱法、扫描电子显微镜结合能量色散X射线光谱法、傅里叶变换红外光谱法、拉曼光谱法、X射线衍射、气相色谱-质谱法、裂解气相色谱-质谱法。

6．技术规范与注意事项

—配有光纤的分光光度计

—光源

—光谱范围

—光谱分辨率

—测量头几何条件（如照明0°、信号采集45°）

—测量区域

—每光谱扫描次数

—校准物（如Spectralon ^® 99%反射标准板）。

7．技术简史

1938年，巴恩斯（Barnes）率先用这种方法凭借颜料的光谱特征来表征颜料。

8．文献

[1] Serefidou M., S. Bracci, D. Tapete, A. Andreotti, L. Biondi, M.P. Colombini, C. Giannini, D. Parenti, ‘Microchemical and Microscopic Characterization of the Pictorial Quality of Egg-tempera Polyptych, Late 14 ^th Century, Florence, Italy’, Microchemical Journal 127, pp.187-198. (2016)

[2] Cheilakou E., M. Troullinos, M. Koui, ‘Identification of Pigments on Byzantine Wall Paintings from Crete (14 ^th Century AD) using Non-invasive Fibre Optics Diffuse Reflectance Spectroscopy (FORS)’, Journal of Archaeological Science 41, pp. 541-555. (2014)

[3] Gulmini M., A. Idone, E. Diana, D. Gastaldi, D. Vaudanc, M. Aceto, ‘Identification of Dyestuffs in Historical Textiles: Strong and Weak Points of a Non- invasive Approach’, Dyes and Pigments 98, pp. 136-145. (2013)

[4] ‘On-line Database of Fibre Optics Reflectance Spectra (FORS) of Pictorial Materials in the 270-1700 nm range’. (2011) http://fors.ifac.cnr.it/ (Retrieved 25-09-2017)

[5] Delaney J.K., G.Z. Jason, M. Thoury, R. Littleton, M.R. Palmer, K.M. Morales, E.R. de la Rie, A. Hoenigswald, ‘Visible and Infrared Imaging Spectroscopy of Picasso’s Harlequin Musician: Mapping and Identification of Artist Materials In Situ’, Applied Spectroscopy 64, pp. 584-594. (2010)

[6] Bacci M., L. Boselli, M. Picollo, B. Radicati, ‘Ultraviolet, Visible, Near Infrared Fibre Optics Reflectance Spectroscopy’, in Scientific Examination for the Investigation of Paintings (ed. D. Pinna, M. Galeotti, R. Mazzeo), pp. 197-200. (2009)

[7] Bacci M., A. Casini, C. Cucci, M. Picollo, B. Radicati, M. Vervat, ‘Non-invasive Spectroscopic Measurements on the II Ritratto della Figliastra by Giovanni Fattori: Identification of Pigments and Colorimetric Analysis’, Journal of Cultural Heritage 4 (4), pp. 329-336, (2003)

[8] Leona M., J. Winter, ‘Fibre Optics Reflectance Spectroscopy: A Unique Tool for the Investigation of Japanese Paintings’, Studies in Conservation 46 (3), pp. 153-162. (2001)

[9] Bacci M., ‘UV-Vis-NIR FORS Spectroscopies in Modern Analytical Methods in Art and Archaeology’, in Chemical Analysis Series Vol. 155 (ed. E. Ciliberto, G. Spoto), New York: Wiley & Sons, pp. 321-361. (2000)

[10] Picollo M., M. Bacci, A. Casini, F. Lotti, S. Porcinai, B. Radicati, L. Stefani, ‘Fibre Optics Reflectance Spectroscopy: A Non-destructive Technique for the Analysis of Works of Art’, in Optical Sensors and Microsystems: New Concepts, Materials, Technologies (ed. S. Martellucci, A.N. Chester, A.G. Mignani), New York: Kluwer Academic/Plenum Publishers. (2000)

[11] Barnes N.F., ‘A Spectrophotometric Study of Artists’ Pigments’, Technical Studies in the Field of Fine Arts 7, pp. 120-138. (1938)