FORS, Fiber Optics Reflectance Spectroscopy for Pigments Identification

FORS (Fiber Optics Reflectance Spectroscopy) has been used for art examination and art conservation for at least 2 decades for identification of pigments [1, 2, 3, 4] and dyestuffs [5]. The strength of this method is the relatively simplicity of the equipment: a source of light, a spectrometer and 2 fibers optics, one to deliver the light on the object and the other to collect the light reflected.  A Reflectance spectrum shows for each wavelength the ratio between the intensity of the reflected light and the intensity of the incident light.

I was following the development of a series of miniaturized spectrometers by Ocean Optics, a leader in innovative optical systems. As for my daily work in on-site art examination, I’m always looking for new low-weight solutions and these instruments looked as exactly what I was searching.  I wrote to Ocean Optics and they put me in contact with their Italian representative, GHT Photonics, based in Padua, the town where Giotto decorated the Scrovegni chapel, one of his most famous frescoes. They were helpful to arrange a loan and let me have a look at their low-cost FORS system in the “Cultural Heritage Science Open Source” lab in Sicily. I was so delighted with this system. Ocean Optics has made a kind of revolution in spectroscopy: miniaturized and low-cost spectrometers, really, really affordable. 

This opens possibilities to researchers and private professionals which can now introduce optical spectroscopy in their workflow. Indeed, with just one spectrometer it is possible to run a different number of spectroscopic methods, just changing lamps and probes. The same spectrometer can be used for reflectance spectroscopy and transmittance spectroscopy as well as fluorescence spectroscopy. So, just purchasing one spectrometer and using some of our geekiness with optical tools we can run a number of art examinations. Should I use one word to describe this system, I would say FUN!

I have been testing this FORS system on my collection of historical pigments and on a number of art objects in Sicily and I’ll provide some results in the following posts. This video shows some of the art examined.

Gorgias – Reflectance Spectroscopy system

References

[1] T. Cavaleri, A. Giovagnoli, M. Nervo “Pigments and mixtures identification by Visible Reflectance Spectroscopy”  Procedia Chemistry   8  ( 2013 )  45 – 54.

[2] E. Cheilakou, M. Troullinos, M. Koui “Identification of pigments on Byzantine wall paintings from Crete (14th century AD) using non-invasive Fiber Optics Diffuse Reflectance Spectroscopy (FORS)” Journal of Archaeological Science 41 (2014) 541-555.

[3] M. Picollo, M. Bacci, A. Casini, F. Lotti, S. Porcinai, B. Radicati, L. Stefani “Fiber Optics Reflectance Spectroscopy: a non-destructive technique for the analysis of works of art” Optical Sensors and Microsystems: New concepts, Materials, Technologies, edited by Martellucci et al., Kluwer Academic / Plenum Publishers, New York, 2000

[4] Scientific examination for the investigation of paintings, AA.VV.Edited by D. Pinna, M. Galeotti, R. Mazzeo, 2009.

[5] M. Gulmini, 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 (2013) 136-145.