## 3 Results and Discussion  
In this work, Raman investigations have been performed on a representative specimen of the frame of the oil painting \"White Man's Buffalo\". The investigated specimen labeled as N. 01.1622, was extracted from the upper left inside corner of the frame as indicated by the red area shown in Figure 1a and the actual sample studied is depicted in Figure 1b. To collect spectroscopic data, a representative division of the surface of the specimen into areas to be studied has been adopted. Figure 1c shows the marked sectors that have been subjected to Raman investigations. Figure 1: (**a**) The area investigated (red circle) of the frame from which the specimen was extracted, (**b**) The specimen N. 01.1622 coming from the area shown in (**a**,**c**) Experimental division of the specimen N. 01.1622 into the 10 different sectors representing the mapping of the spots explored by Raman analysis. Raman spectra have been collected on the marked sectors labeled as S1, S2, S3, S4, S5, S6, S7, S8, S9, and S10 in the range from 150 to 4000 cm\({}^{-1}\). The sectors: S7, S8, S9 and S10 were treated by the water gilding technique for the application of the golden leaf. The representative Raman spectra collected on such samples are shown in Figure 2.  
Figure 2: Representative Raman spectra of the specimen N. 01.1622 collected on the 10 sectors labeled as (**a**) S1, (**b**) S2, (**c**) S3, (**d**) S4, (**e**) S5, (**f**) S6, (**g**) S7, (**h**) S8, (**i**) S9 and (**l**) S10 in the spectral range from 150 to 4000 cm\({}^{-1}\), and by using a laser source at 514 nm. The representative Raman spectrum collected on the S1 sector (spectrum a) is characterized by the vibrational bands located at 218 and 281 cm\({}^{-1}\) which can be assigned to the red pigment of hematite, Fe\({}_{2}\)O\({}_{3}\)[15; 16; 17]. The broadband with the two modes at about 1364 and 1559 cm\({}^{-1}\) is assigned to the Van Dyck Brown pigment (VDK). The VDK pigment is classified as humic-hearth material, which contains significant content of amorphous carbon matter of the humic earth and a low percentage of iron oxides [16; 18]. Some of these oxides can be ascribed to the presence of the Armenian bole which is fine earth with the typical red color that it is due to its composition of clay and iron oxides [19; 20] and that is mainly used as a preparatory layer of the water gilding technique [19]. The presence of humic substances can be confirmed by the broad, low intensity band falling in the spectral region between 2900 and 3600 cm\({}^{-1}\). The Raman spectrum relative to the S2 sector (spectrum b) comprised the vibrational bands of the hematite and the VDK pigment. The band at 218 cm\({}^{-1}\) can be assigned to Fe\({}_{2}\)O\({}_{3}\), while the broad bands at 1381 and 1563 cm\({}^{-1}\) are due to the VDK pigment. Humic substances can be also detected in the high wavelength region of the spectrum (2900-3600 cm\({}^{-1}\)). The Raman spectrum of the S3 sector (spectrum c) contains the Raman modes of the VDK pigment (1347 and 1584 cm\({}^{-1}\) modes). In the Raman spectrum of the S4 sector (spectrum d), the presence of the hematite, Fe\({}_{2}\)O\({}_{3}\), is given by the following vibrational bands located at 271, 325, and 605 cm\({}^{-1}\). The observed mode at 1090 cm\({}^{-1}\) is ascribed to humic substances [15]. Sector S5 was also investigated, and the Raman spectrum (spectrum e) confirms traces of the VDK pigment, as justified by the Raman modes at 1393 and 1578 cm\({}^{-1}\). The Raman spectrum collected on the S6 sector shows vibrational bands around 267, 618, 1342, and 1553 cm\({}^{-1}\) (spectrum f). The modes at 267 and 618 cm\({}^{-1}\) are once again assigned to the hematite. The modes at 1342 and 1553 cm\({}^{-1}\) can be attributed to the amorphous carbon, typical of the VDK pigment. As previously discussed, the presence of the humic components could be observed in the region between 2900 and 3600 cm\({}^{-1}\).