## 3 Results and Discussions
### The Thermal Modification  
The effectiveness of thermal modification of stone pine wood was evaluated by mass loss, which is considered a reliable index for predicting the increased decay resistance of wood and a predictor of mechanical resistance [36]. Thermal modification causes first holocellulose and then lignin degradation. Holocellulose is the primary nutritional substrate for various rot fungi and is responsible for the hygroscopic behavior of wood [37]. As a result of degradation, we observed a decrease in the oxygen/carbon (O/C) ratio in wood caused by the formation of carbonaceous materials [38]. At the highest temperature, the degradation of lignin compounds is also involved [39]. Figure 2 shows the different colors of wood species for untreated wood and for each treatment temperature (180, 195, 210, 220, and 240 \({}^{\circ}\)C). All wood species became darker and browner with increasing temperature. Even at lower treatment temperatures, Stone pine's heartwood showed significant stains caused by the resin exudates (column D in Figure 2). Darker woods of tropical species were always considered prestigious and luxurious goods. However, due to the decreased availability of tropical species, as well as to the restrictions introduced in their trade, heat-treated wood can be considered a valuable alternative to be appreciated by the consumers [40,41]. As an example, it is possible to state that as the temperature rises, there is a pronounced decrease in the L* component (Figure 3). Comparing Figures 2 and 3, it is evident that the greater the darkening, the lower the L* coordinate value. The decreasing rate of the L* coordinate in stone pine sapwood was comparable to the control species, while in stone pine heartwood, the abrupt decrease in L* was more evident already at the lower temperature. Table 2 shows the percentage of mass loss for each wood species and each maximum treatment temperature. The sapwood and heartwood of stone pine were compared with beech and Scots pine wood. The higher the treatment temperature, the higher the percentage of mass loss. At 180 \({}^{\circ}\)C, the heartwood of stone pine showed a mass loss of 9.67 \(\pm\) 2.84%, the highest among the wood species considered. There were no previous studies on the thermal modification of stone pine heartwood. It is known that the final performances depend on the heating protocol. However, [PERSON], et al. [37] showed that Maritime pine and Aleppo pine release terpen during heating, such as hexanal, beta-pinene, camphene, nonanal, isobornyl acetate, carophyllene, humulene, and carophyllene oxide, which were identified as predominant compounds. Due to the high resin content in pine wood, it is assumed that the behavior is similar to the results obtained by [PERSON], et al. [37],  
Figure 2: Thermally modified samples: Scots pine (**A**), beech (**B**), stone pine sapwood (**C**), stone pine heartwood (**D**). and the higher decrease in mass is to be attributed to the volatilization of the resin. In the case of stone pine, no comparison can be made with our investigation as there are no previous studies, only Corsican pine (_Pinus nigra_ subsp. _laricio_ (Poir.) Maire) wood was studied in Italy [42]. In the case of beech wood, other authors using a different thermal modification treatment observed a lower mass loss than in our study [43], and it is not possible to establish a reliable comparison. Under the most severe heating conditions (above 200 \({}^{\circ}\)C), hemicellulose decomposition with acetic acid production and the presence of initial lignin degradation products such as vanillin and guiaacyclactone can be assumed in pines, which are also present in other Mediterranean pines [37]. These compounds have also been detected in Corsican Pine by Py-GC/MS [44]. Up to 220 \({}^{\circ}\)C, the sapwood of stone pine showed comparable values for mass loss as that of Scots pine. At a temperature of 240 \({}^{\circ}\)C, the sapwood of stone pine showed a higher mass loss (19.56 \(\pm\) 2.30%) than that of Scots pine (15.75 \(\pm\) 1.57%).