FORS, Reflectance Spectroscopy for pigments. BWTEK mini spectrometer

Just tested the low-cost mini spectrometer from BWTEK, Quest U (BRC112P-U). This is the most affordable of BWTEK series of  mini spectrometers. It features a 2048 pixels linear array and covers the 200 -850 nm range. This test was done in collaboration with MADATEC, an Ital­ian com­pany sup­ply­ing sci­en­tific imag­ing and ana­lyt­i­cal equip­ment also for art conservation sector . CHSOS already tested an ultraviolet lamp based on high power UV LEDs developed by MADATEC.

CHSOS welcomes companies to collaborate to evaluate their instruments for the specific tasks of art  examination. MADATEC assembled this FORS system (Fiber Optics Reflectance Spectroscopy) : the  Quest U mini spectrometer was coupled with a fiber optical reflectance probe including seven 200 microns fibers and a tungsten light source.


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’.


reflectance spectroscopy pigments FORS

FORS system for pigments identification. BWTEK Quest U spectrometer coupled with a fiber optical reflectance probe including seven 200 microns fibers and a tungsten light source.

This FORS system was tested on the pigments checker laid with egg tempera, a collection of 54 historical pigments. The results are compared with the online FORS database of historical pigments published on e-conservation Journal.

The tested system delivers spectra (red  curves in the following images) comparable to those of the online database. We are comparing them with the spectra of the swatches laid with gum arabic since they were acquired with a similar probe.

These examples show that the Quest U is a valid spectrometer for reflectance spectroscopy of pigments. The exposure time was 30 ms with 10 averages and boxcar 5.

lithopone

Lithopone is a mixture of barium sulfate, a good flat reflector and zinc sulfide. This last one is responsible for the absorption bands in the 650-800 nm region which are well represented by the Quest U system.

titanium

Titanium white features a strong UV absorbance which is evident in the Quest U FORS spectrum.

smalt

Smalt is characterized by a wide absorbance band between the green and red region and a tiny maximum at 560 nm, detected by the Quest U spectrometer.

 

chrome green

Chrome green features two absorption bands at 450 nm and one in the UV at 380 nm. This resulting maximum is therefore challenging to detect. Quest U does a perfect job.

yellow ochre

Yellow ochre features a characteristic S- shape and the presence of two broad absorption bands near 660 nm and 930 nm which are attributed to goethite.

[ws_table id=”7″]
2016-10-17T16:33:12+00:00

Leave A Comment

Time limit is exhausted. Please reload CAPTCHA.