## 3 Results and Discussion
### Color Measurements  
Initially, the means of the colorimetric parameters L\({}^{*}\), a\({}^{*}\), b\({}^{*}\), C\({}^{*}\), and h\({}^{\circ}\) of teak wood before thermal modification were 53.87, 11.52, 23.41, 26.09, and 63.80\({}^{\circ}\), respectively. They \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Treatments** & **Total Extractives (\%)** & **Dichloromethane Extractives (\%)** & **Acetone Extractives (\%)** \\ \hline Untreated & 8.50 c & 4.25 b & 2.15 d \\  & (2.11) & (5.07) & (1.52) \\ \hline CS160 & 15.17 a & 8.50 a & 7.79 a \\  & (0.55) & (2.84) & (1.21) \\ \hline OS185 & 7.71 d & 1.76 c & 2.72 c \\  & (0.79) & (2.83) & (0.83) \\ \hline OS210 & 8.59 b & 4.61 b & 4.39 b \\  & (1.09) & (3.11) & (3.91) \\ \hline Shapiro–Wilk test & 0.88 ns & 0.57 ns & 0.14 ns \\ \hline Bartlett test & 0.54 ns & 0.33 ns & 0.08 ns \\ \hline F test & 2806.7 * & 728.02 * & 4020.1 * \\ \hline r & 0.994 * & 0.911 ns & 0.968 * \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Means of extractive content according to the solvent. were calculated based on data from all 45 samples (three groups of 15, Figure 1) before thermal modification. According to the classification of [PERSON] and Goncalez [28], the color of untreated teak wood was classified as \"light brown\". This was the same color as reported by [PERSON] et al. [17] for teak wood from Myanmar. Although the authors did not provide extra information about the material (e.g., tree age, planted x natural forests), it is likely to be heartwood because of the lightness result (47.0). [PERSON] et al. [39] and [PERSON] et al. [40] stated that secondary metabolites influence the color and smell of teak wood. Extractives contain chromatic compounds, such as phenolic hydroxyl groups, carbonyl groups, and double bonds, which impart color to the wood. In the specific case of teak, the unique color is promoted by the presence of 2-methyl-anthraquinone. The results of the mean colorimetric parameters L*, a*, and b* are plotted in Figure 6, where it is possible to see that the wood before the thermal modification is grouped close to each other, indicating that they had a similar color. This was expected according to the design of the initial sampling (Figure 1). However, the color of untreated wood for each treatment had a different classification [28], as can be seen in Figure 7. Although this difference is not too perceptible to human vision, the method adopted identified three different colors, which indicates how sensitive it is. TMW shifted downward to different positions in Figure 6 from its respective untreated wood, indicating the effect of the process on the original wood color. According to the classification of \(\Delta\)E*, the change in wood color after thermal modification was \"much\" (from 6.1-12.0, Table 3) for all treatments. In Figure 8, it is possible to see that the means of \(\Delta\)E* were 19.74, 11.65, and 15.37, respectively, for 160 CS, 185 OS, and 210 OS. Indeed, the means of \(\Delta\)E* of 160 CS and 210 OS did not fit the scale presented in Table 1, which suggests that, for thermally modified wood, the scale should be enlarged. We highlight that the classification was not designed for analyzing the color change of TMW but rather for weathered wood [29]. Although 160 CS had a higher \(\Delta\)E*, it was lower than that reported (24.11) by [PERSON] et al. [21], who studied the same closed-system process and temperature. Figure 6: Three-dimensional graphic positioning for each treatment. Treatments marked with “u” mean wood before thermal modification (untreated). Anyway, TMW became darker compared to the untreated wood, which is represented by the reduction in lightness (\(\Delta\)L*) for all treatments (Figure 8) and can be seen in the color chart presented in Figure 7. According to the results of other studies [14; 18; 19; 21], the reduction in lightness is the most relevant color change related to thermally modified teak wood, which was also verified in our work.