## 3 Results  
### Characteristic Temperatures  
The first test was performed to determine the maximum firing temperature. Raw, dried glazes and a high-temperature microscope were used for this purpose. The results of these measurements are presented in Figure 1 (sinterability curves) and Table 2 (shrinkage of the measured sample at the chosen temperatures). The obtained sinterability curves can be divided into three groups. The first is the sinterability curves for glazes 1 and 3, for which the melting of these glazes is achieved at the highest temperatures. For glaze 1, it may indicate a weaker effect of sodium oxide as a flux, while for glaze 3 it seems to be different from the assumptions. For a molar ratio of sodium oxide to potassium oxide equal to 1, the characteristic temperatures should be significantly reduced, and glaze melting was achieved faster due to the composition corresponding to the eutectic mixture. In this case, it is not observed. The second group of glazes is glazes 2 and 4, with twice the amount of sodium or potassium oxide in the second oxide. In this case, the curves are very similar, with a slightly stronger fluxing effect of the Na\({}_{2}\)O/K\({}_{2}\)O = 2.0 mixture, that is, when sodium oxide is predominant in the composition. The third group is glaze 5, with a significant predominance of potassium oxide in its composition, for which the sinterability curve decreases the fastest with increasing temperature. This may indicate a much stronger fluxing effect of potassium oxide, especially when it is the main monovalent oxide of a fluxing nature. This is also observed when comparing the sinterability values at selected temperatures (Table 2). Characteristic temperatures were designated based on the geometric dimensions of the samples. The sintering temperature is the temperature at which the onset of dimensional changes in the sample is observed. The sphere, half-sphere, and melting temperatures are determined when the sample reaches the same, half, and one-third of the sample base length, respectively. The characteristic shape of the sample is caused by the forces of surface tension and viscosity of the glaze. The characteristic temperatures (Figure 2) illustrate the differences described above. The highest sintering temperature was obtained for glaze 3 with an equal molar ratio of sodium oxide to potassium oxide, while the lowest values were observed for glazes 2 and 4, or for those for which the amount of sodium oxide or potassium oxide was twice as high as the second. The differences between designated characteristic temperatures are not very high, suggesting that the sodium and potassium oxides (changing molar ratio) and their flux acting are not very strong in this type of glazes. In the case of other temperatures, a stronger fluxing effect of potassium oxide is observed, i.e., a decrease in individual characteristic temperatures with an increase in the amount of potassium oxide in the glaze composition. The exception to this rule is glaze 3 (equimolar amounts of sodium oxide and potassium oxide), for which a slightly \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Glazes**} & \multicolumn{5}{c}{**Shrinkage [\%]**} \\ \cline{2-6}  & **1100** & **1150** & **1200** & **1250** & **1300** \\ \hline Glaze 1 & 99.5 & 97.4 & 86.6 & 81.7 & 46.2 \\ Glaze 2 & 99.5 & 95.2 & 84.4 & 66.5 & 38.0 \\ Glaze 3 & 101.1 & 97.9 & 83.5 & 79.3 & 45.8 \\ Glaze 4 & 99.8 & 95.2 & 87.4 & 70.9 & 37.9 \\ Glaze 5 & 100.4 & 93.3 & 81.9 & 54.4 & 34.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Shrinkage of the measured sample at the chosen temperatures. Figure 1: Sintering curve of HSM measurements showing changes in the geometric dimensions of samples (Na\({}_{2}\)O/K\({}_{2}\)O ratio in brackets). higher temperature was recorded (but still lower than for glaze 1), which deviated from the described trend.