# FUXYA2020: A Low-Cost Homemade Portable EDXRF Spectrometer for Cultural Heritage Applications
## 3 FUXYA2020 Performance on Real Cases in Cultural Heritage Field
### Pigments  
In the last 20 years, EDXRF has proved to be a very suitable and widely used tool for the examination of paintings, also for its fast response and its totally non-invasive character [47]. Analysis of pigment layers using the FUXYA was conducted on laboratory-made panels (Figure 7), choosing single layers (monolayers) of historical and modern pigments, as reported in Table 2. The unfiltered tube spectrum was used as incident radiation, thanks to the low background of the instrument at low energies. The operating conditions were 40 kV and 0.06 mA, with an acquisition time of 200 s for each measurement. As many factors influence the pigment stratigraphy (binder, dilution, and thickness of the layers, which also depend on many factors) when dealing with pigment layers, it is more useful and sensible to perform a qualitative analysis, as a quantitative analysis is not only not feasible but will not be useful to characterize the nature of the pigment. Figure 6: FUXYA spectrometer and its internal set up. Figure 7: Analysis of pigment layers by FUXYA spectrometer: the laser beam for positioning and the red light indicating the correct distance are visible. Test panels of pure pigment layers were painted on different substrates, with different binders: panel A (binder: egg tempera) is a wooden board with gypsum preparation, while panel B (acrylic binder) is an industrial canvas applied on cardboard. The pigments used for these tests were natural and artificial lapis lazuli, malt blue, cobalt blue, azurite, verdigris, titanium green, unber, lead yellow, minium, cinnabar, red ochre, burnt sienna (panel A) and cerulean blue, Naples yellow, malachite, cinnabar, chromium orange (panel B). As the pigments layers are very thin, during an XRF measurement is possible to detect elements coming from the preparation underneath (except in cases where heavy metals are used, such as lead), thus preparation of both panels was also investigated as reference. For panel, A, Ca, Sr and S traces were detected from gypsum preparation, with impurities of P, Fe, Cu, Zn, Zr; for panel B, the analyses determined the presence of titanium white (Ti dioxide) and Ca, with impurities of P, Fe, Cu, and Zn. These elements are reported in Table 2 only when attributable to pigment layers; each spectrum also presents the K emission of Ar from the atmosphere. As evident from Table 2, all pigments were positively detected within the XRF limits, except sample B6, Mount Amiata cinnabar, which revealed itself to be a case of forgery, as no presence of Hg (nor any other red chromophore) was detected. The barium presence can be attributed to barium sulphate, commonly used as a pigment extender with lakes. A rapid check with other analytical techniques confirmed the use of a red lake with a mixture of white pigments, coherently with FUXYA results. Further comments should also be done on sample A12, burnt sienna earth, where Mn could be expected. Indeed, sienna is a yellow ochre, containing from 50% to more than 70% iron oxide (Fe\({}_{2}\)O\({}_{3}\)), (the higher the iron concentration, the better the quality) [47] and, even if it is often considered a mixture of Mn and Fe oxides, Mn oxide (gray or black in color) is quite low, and it is present in quantities up to 10% [48], while a greater amount of Mn oxides are typical of numbers. Coherently, some spectra databases [49] indicate sienna earth also in the absence of Mn. In Figure 8, the spectra acquired with FUXYA spectrometer on lapis lazuli layered pigment (sample A1 in Table 2) is reported; the Si K\(\alpha\) lines are evident in the enlargement of low energy region.