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.


FORS Fiber Optics Reflectance Spectroscopy , prints, drawings, stamps, manuscripts, wall paintings, pigments, paintings conservation, paintings authentication, Technical Art Examination

FORS, Fiber Optics Reflectance Spectroscopy system from Ocean Optics. Halogen lamp (left), USB4000 spectrometer (center), probe (right).


pigments checker v2 vsPigments Checker is for photographers, conservators and scientists interested in technical documentation of paintingss. It has 54 swatches of historical pigments designed for infrared photography, ultraviolet photography and other technical photographic methods for art examination. Check it out!

Pigments Checker is a collection of 54 swatches of his­tor­i­cal pig­ments that have been applied using gum ara­bic as a binder on a cel­lu­lose and cot­ton water­color paper, acids and lignin free. This paper is not treated with opti­cal bright­en­ers, it’s slightly UV flu­o­res­cent, and it reflects IR. Two cross-hair lines, 0,2 mm (ver­ti­cal) and 0.4 mm (hor­i­zon­tal) are printed on each swatch of paper before the appli­ca­tion of paint, in order to have a means to eval­u­ate the pig­ments’ trans­parency in the IR and IRR imag­ing. Among all the pig­ments and their vari­eties ever used in art these pig­ments col­lec­tion select the most used ones from antiquity to early 1950’.

I was following the development of a series of miniaturized spectrometers by Ocean Optics, 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 Photonicsbased 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 by this system. Ocean Optics has made a kind of revolution in spectroscopy: miniaturized and low-cost spectrometers, really, really affordable. 

FORS Fiber Optics Reflectance Spectroscopy, FORS Fiber Optics Reflectance Spectroscopy , prints, drawings, stamps, manuscripts, wall paintings, pigments, paintings conservation, paintings authentication, Technical Art Examination

Ocean Optics USB4000 miniaturized spectrometer, stands in one hand.

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 geekeness 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.


CHSOS newsletter



[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 weakpoints of a non-invasive approach” Dyes and Pigments 98 (2013) 136-145.

[ws_table id=”7″]


  1. Antonio Martinez March 1, 2014 at 12:58 am - Reply

    Saludos, I just discovered your website and I think it is excellent! Where can I get the paint chart you use in the video?

  2. Antonino Cosentino July 30, 2014 at 2:14 pm - Reply

    Hi Antonio, The paint chart are made with Kremer pigments. You can make them on your own (buying the Kremer pigments, the product codes are in the chart itself). I prepare themas a gift for those who take my training program in multispectral imaging and technical photography for art examination.

  3. […] Rimandiamo per una descrizione completa dell’apparato e della sua applicazione alle parole dello stesso Dott. Cosentino all’indirizzo […]

Leave A Comment

Time limit is exhausted. Please reload CAPTCHA.