## 3 Results and Discussion
### Color Measurements
All structural cell wall components, as well as extractives, can contribute to changing the wood color. The darker color can be attributed to the formation of hemicellulose degradation products (except in the case of OS185), changes in the extractives, and the formation of oxidation products, such as quinones, as well as the percolation of extractives to the samples' surface [17; 41]. Variations in L*, a*, and b* coordinates followed the same trend as \(\Delta\)E*, with greater absolute variation (in modulus) in CS160 and lesser variation in the OS185 treatment. This highlights the smaller effect of thermal modification on the red-green (a*) pigmentation of  
Figure 8: Variations in colorimetric parameters by treatment. Figure 7: Classifications of color and total color variation (\(\Delta\)E*). 1 [PERSON] et al. [29]. 2 [PERSON] and [PERSON] [28]. teak wood when compared to the yellow-blue (b*) pigmentation, which was also verified in other studies [18; 19; 21]. Despite the absolute means and the different colors before thermal modification (Figure 7), the TMW of CS160 and OS210 achieved the same color (\"dark brown\"). Notice how close these treatments are in Figure 6 when compared to OS185. This result was unexpected, considering that CS160 and OS210 were carried out with different temperatures and processes, which resulted in different corrected mass losses (Figure 5), as well as different extractive contents (Table 5). However, since \(\Delta\)E* was higher for CS160 (19.74) than for OS210 (15.37), if the wood color of both treatments was the same before thermal modification, TMW CS160 would likely be darker. But this hypothesis needs further investigation. Based on the results of CS160 and OS210, it seems that the CML is not related to the color of TMW from different processes. On the other hand, it makes sense when comparing TMW from the same treatment, as OS210 had higher CML and \(\Delta\)E* than OS185. This pattern was verified by other authors in open-system thermal modification, i.e., the increase in temperature resulted in increased \(\Delta\)E* [17; 18; 19]. [PERSON] et al. [11] provided a literature review and discussed that there is a good dependency between mass loss, chemical composition, fungal durability, and hygroscopicity. However, these relations cannot be directly transferred to other properties, such as color, and further investigation on this topic is necessary. Even the mildest condition of thermal modification (OS185) was able to change the color of TMW (\(\Delta\)E* = 11.65) compared to untreated wood. This result was similar to those obtained in open-system processes at 180 \({}^{\circ}\)C by other authors [17; 18], which were, respectively, 9.67 and 11.97. There was no significant difference in the chemical composition of the cell wall components between untreated wood and OS185 (Table 4). On the other hand, there was a significant difference in the extractive content between untreated wood and OS185 (Table 5), where the most relevant (reduction in 2.49 p.p.) was in the dichloromethane content. Thus, it seems that the combined effect of the volatilization of apolar extractives and the drying of hygroscopic water (from 11.48% to 0.43%, Figure 4) was responsible for this color change. Notice that this drying effect also happened in treatments CS160 and OS210.