## 3 Results
### Reflectance Values at a Wavelength of 1000-1700 nm
In the assessment of differences in reflectance values at subsequent time points (before oil application, after 20 min, and after 60 min), a statistically significant difference (\(p\) < 0.0001) was found between particular time points for the reflectance at a wavelength of 1000-1700 nm after the application of Oil C.  
It was found that at a wavelength of 1000-1700 nm after the application of Oil C (Table 12), the reflectance value after 20 min of exposure was statistically significantly lower compared with the value before exposure and with the values after 60 min and 120 min of exposure, and the reflectance value after 120 min of exposure was statistically significantly higher compared with the value after 20 min and 60 min of exposure. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \begin{tabular}{c} **Wavelength:** \\ **1000–1700 nm** \\ \end{tabular} & **Variable** & **Mean** & **Median** & **Min.** & **Max.** & **Q 25\%** & **Q 75\%** & \
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} &
\begin{tabular}{c} **Shapiro–Wilk** \\ **Test** \\ \end{tabular} \\ \hline Oil A before & A\_0 & 0.285 & 0.285 & 0.264 & 0.311 & 0.277 & 0.293 & 0.014 & \(p\) = 0.4306 \\ \hline Oil A after 20 min. & A\_20\_min & 0.277 & 0.276 & 0.235 & 0.311 & 0.270 & 0.288 & 0.016 & \(p\) = 0.6017 \\ \hline Oil A after 60 min. & A\_60\_min & 0.292 & 0.287 & 0.259 & 0.370 & 0.279 & 0.293 & 0.027 & \(p\) = 0.0011 \\ \hline Oil A after 120 min. & A\_120\_min & 0.301 & 0.293 & 0.259 & 0.369 & 0.278 & 0.323 & 0.030 & \(p\) = 0.1832 \\ \hline Oil B before & B\_0 & 0.288 & 0.288 & 0.266 & 0.311 & 0.279 & 0.297 & 0.013 & \(p\) = 0.8687 \\ \hline Oil B after 20 min. & B\_20\_min & 0.280 & 0.281 & 0.259 & 0.302 & 0.274 & 0.288 & 0.010 & \(p\) = 0.0998 \\ \hline Oil B after 60 min. & B\_60\_min & 0.295 & 0.289 & 0.263 & 0.357 & 0.280 & 0.299 & 0.025 & \(p\) = 0.0074 \\ \hline Oil B after 120 min. & B\_120\_min & 0.305 & 0.297 & 0.263 & 0.357 & 0.285 & 0.335 & 0.029 & \(p\) = 0.1123 \\ \hline Oil C before & C\_0 & 0.288 & 0.283 & 0.270 & 0.309 & 0.277 & 0.302 & 0.014 & \(p\) = 0.0221 \\ \hline Oil C after 20 min. & C\_20\_min & 0.278 & 0.275 & 0.231 & 0.306 & 0.272 & 0.291 & 0.017 & \(p\) = 0.0806 \\ \hline Oil C after 60 min. & C\_60\_min & 0.298 & 0.290 & 0.265 & 0.360 & 0.280 & 0.308 & 0.028 & \(p\) = 0.0104 \\ \hline Oil C after 120 min. & C\_120\_min & 0.305 & 0.301 & 0.266 & 0.364 & 0.279 & 0.335 & 0.031 & \(p\) = 0.0577 \\ \hline Oil D before & D\_0 & 0.288 & 0.285 & 0.271 & 0.309 & 0.277 & 0.297 & 0.012 & \(p\) = 0.1109 \\ \hline Oil D after 20 min. & D\_20\_min & 0.282 & 0.284 & 0.244 & 0.306 & 0.274 & 0.293 & 0.015 & \(p\) = 0.2778 \\ \hline Oil D after 60 min. & D\_60\_min & 0.298 & 0.290 & 0.266 & 0.361 & 0.280 & 0.306 & 0.027 & \(p\) = 0.0098 \\ \hline Oil D after 120 min. & D\_120\_min & 0.308 & 0.303 & 0.266 & 0.367 & 0.283 & 0.340 & 0.032 & \(p\) = 0.0817 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Selected descriptive statistics of the reflectance value at a wavelength of 1000–1700 nm, along with a statistical assessment of the normality of distribution. In the assessment of differences in reflectance values at subsequent time points (before oil application, after 20 min, and after 60 min), a statistically significant difference (\(p=0.0094\)) was found between particular time points for the reflectance at a wavelength of 1000-1700 nm after the application of Oil D.  
It was found that at a wavelength of 1000-1700 nm after the application of Oil D (Table 12), the reflectance value after 120 min of exposure was statistically significantly higher compared with the value after 20 min of exposure. Comparing the type of oil, there was no statistically significant difference in the values of reflectance at a wavelength of 1000-1700 nm before exposure (\(p=0.9319\)), after 20 min of exposure (\(p=0.5504\)), after 60 min of exposure (\(p=0.7551\)), and after 120 min of exposure (\(p=0.8877\)) between the type of oil used.