## 4 Results and Discussion
### Raman Spectra  
Besides FTIR spectra, the study of ceramics has been completed with Raman spectroscopy, as can be seen in Figure 7, useful for identifying and classifying the artifacts according to socio-cultural and compositional criteria, and raw material sources [48].  
Of real interest is the Raman signature of the silicate matrix consisting of two pairs of bands: the first between \(\sim\)850 and 1200 cm\({}^{-1}\) and the second between 400 and 600 cm\({}^{-1}\), being attributes of the silicate vibrational unit, the SiO\({}_{4}\) tetrahedron. As can be seen, the spectrum is a fingerprint of the nanostructure of the amorphous silicate network.  
The peaks at 475 cm\({}^{-1}\) in P1 and 476 cm\({}^{-1}\) in P2 are noteworthy as they closely align with the diagnostic peak of 480 cm\({}^{-1}\) associated with iron-bearing mineral oxides. This indicates a potential presence of such minerals in the sample, further corroborating the mineral composition findings. The proximity of these peaks to the known diagnostic peak strengthens the identification of iron-bearing mineral oxides within the sample [49].  
The white color observed in the sample is likely attributed to quartz, as indicated by the presence of peaks at 443 and 465 cm\({}^{-1}\) at P1. Additionally, the band at 1331 cm\({}^{-1}\) is indicative of graphite, which contributes to the composition and characteristics of the material under study. These findings help in identifying the mineral components within the sample and provide insights into its physical properties [50; 51]. The band at 972 cm\({}^{-1}\) is a stretching vibration of the SiO\({}_{4}\) tetrahedra in the structural chain.  
The average intensity band at 583 cm\({}^{-1}\), characteristic of feldspars, serves as the representative Raman band in the analysis. In addition, the presence of hematite is suggested by the band at 508 cm\({}^{-1}\) along with the shoulder around 583 cm\({}^{-1}\), with these features being more pronounced in the red sample. These findings provide crucial insights into the mineral composition of the samples, pointing towards the presence of feldspars and hematite, with variations observed between the red and other samples.  
The broad band around 1350-1500 cm\({}^{-1}\) is due to amorphous carbon, and the band at 461 cm\({}^{-1}\) is attributed to \(\beta\)-quartz. The band at 1331/1323 cm\({}^{-1}\) was recorded as belonging to hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)), as a crystalline phase of iron, for red ocher [52].  
The bands from 1328-1370 cm\({}^{-1}\) and 1594-1597 cm\({}^{-1}\) are indicative of the presence of carbon black within the sample. Additionally, the band detected at 970 cm\({}^{-1}\) may be associated with a broad P-O stretching band, as illustrated in Figure 6. These identified bands provide valuable information regarding the composition and molecular structure of the material under investigation, contributing to a more comprehensive understanding of its properties [53; 54].  
Moreover, besides the hematite and gypsum, specific oil compounds were identified on the ceramic surface, indicating their application as a primer before painting using the dry oil technique. The detection of residual oil traces was linked to a characteristic vibration at 1866/1872 cm\({}^{-1}\), attributed to the C-C stretching of cyclopropenoid compounds found in certain fatty acids present in the straw used as a degreaser. This finding has enabled the identification of oils derived from plants, aiding in estimating the initial oil content and its degradation over time, providing valuable insights into the materials and techniques used in the creation of the artwork [55].