## 3 Results
### Middle Infrared Spectroscopy (MIR) Measurements  
Figure 8 shows the infrared spectra for the pure crystalline phases from the RUFF database, whereas Figure 9. presents all measured mid-infrared spectra. For a more detailed analysis, each spectrum was subjected to a process of decomposition into component bands. The results of the spectral distribution for glazes 1 and 5 are presented in Figures 10 and 11, while all the component bands of the spectral decomposition are presented in Table 4.  
Changes in the structural analysis of these glazes can be difficult to trace due to the presence of crystalline phases and their bands. They will overlap the strands originating from the amorphous phase of the glaze. Figure 8: MIR spectrum of zirconium silicate (blue curve), zirconium oxide (brown curve), and and anesine (light green curve). Figure 7: The image of microstructure of glaze 5 with EDS analysis (5000\(\times\) magnification). Figure 10: MIR spectrum of glaze 1 with decomposition into component bands. Figure 9: MIR spectrum of glazes 1–5 with band positions. In Table 4, all the component bands obtained during the spectral decomposition are shown. For glaze 1, a band corresponding to sigma vibrations (O-Zr-O) can be observed in zirconium silicate (434 cm\({}^{-1}\)). In the analysis of this band, a decrease in integral intensity can be observed for glazes 4 and 5, for which smaller amounts of zirconium silicate are also detected (Table 3). For the 467 cm\({}^{-1}\) band, there is also a shift in the band's position toward lower wavenumbers with a simultaneous increase in its integral intensity for glazes 4 and 5. These bands correspond to sigma (O-Si-O) vibrations, which may indicate an increase in the amount of this kind of bond and a shift toward a lower wavenumber in glazes with a higher potassium oxide content, which may suggest the decomposition of the internal structure. The analysis of the spectrum after decomposition allowed us to observe the presence of the 524 cm\({}^{-1}\) band, which appears only for the glaze 5, and is related to the vibrations occurring in the zirconium oxide--stretching vibration of the bond (Zr-O-Zr). Its appearance is associated with the presence of zirconium oxides (monoclinic and tetragonal varieties). Another group of bands corresponds to vibrations of ring structures present in the structure of the amorphous phase and the andesine crystal phase (range 540-690 cm\({}^{-1}\)). In this group of bands, we observe slight shifts in the position of the bands and a decrease in their intensity, especially for glazes 4 and 5. This suggests a lack of such structures in the amorphous phase and, therefore, a greater disorder in the structure of the glassy phase. The bands in the range of 730 to 800 cm\({}^{-1}\) are bands corresponding to the symmetrical stretching vibrations of the aluminum- and silica-oxygen bridges. In this range, slight shifts of the bands and inconsiderable changes in their integral intensity are observed. On the basis of the obtained results, it can be concluded that this range of bands does not suggest any significant changes in the structure of the analyzed glazes. The next part of the spectra contains bands corresponding to asymmetric vibrations stretching the silicon-oxygen and aluminum-oxygen bonds in aluminum and silicon tetrahedrons. For the bands associated with broken aluminum and silica bridges (844 cm\({}^{-1}\) and 909 cm\({}^{-1}\), respectively), a slight shift toward lower wavenumbers can be observed, compared to the glaze 5 (868 and 902 cm\({}^{-1}\), respectively). This may be related to an increase in the disorder of the structure but also to a decrease in the amount of the andesine crystalline phase, the band of which is also present in this region. It may also be due to the presence of a crystal phase of zirconium silicate, for which there is an intense band at 898 cm\({}^{-1}\). Figure 11: MIR spectrum of glaze 5 with decomposition into component bands.