## 3 Results and Discussions
### Vacuum and Full-Cell Method  
The results of impregnation of the different wood species are presented in Table 1, where the average uptake of preservative products is reported, with standard deviation expressed in kg/m\({}^{3}\). Indeed, in Table 1, the mean values are reported with upper cases related to the statistical analysis. The mean values with the same upper case are not statistically different so they belong to the same group.  
Comparing the vacuum and full-cell methods, it can be observed that the full-cell method resulted in the highest uptake in all wood species (spruce, beech, Scots pine, and stone pine); nevertheless, the heartwood in stone pine proved to be very refractory. In the samples treated with the full-cell method, the heartwood of stone pine showed the lowest uptake of Montax 50 (186.07 \(\pm\) 133.45 kg/m\({}^{3}\)), followed by Belocid (230.57 \(\pm\) 28.97 kg/m\({}^{3}\)) and Silvanolin (290.58 \(\pm\) 182.06 kg/m\({}^{3}\)); the values were revealed to be not statistically different from those of spruce (Montax 50 258.76 \(\pm\) 66.27, Belocid 189.33 \(\pm\) 104.02, and Silvanolin 391.50 \(\pm\) 134.16 kg/m\({}^{3}\)). The result is quite remarkable, as spruce is known to be one of the most refractory species due to the presence of aspirated pits in the heartwood and small cells [34]. The low uptake of preservatives in the heartwood of stone pine can be considered irrelevant for practical applications due to the high resin content of this tissue, which provides high wood durability (durability class 2 according to EN 350:2016 [35]), making treatment unnecessary, if not absolutely recommended [19]. The uptake measured using the full-cell method with Belocid was not statistically different between stone pine heartwood (230.57 \(\pm\) 28.97 kg/m\({}^{3}\)) and beech (275.75 \(\pm\) 38.15 kg/m\({}^{3}\)). It could be assumed that the organic solvent of Belocid dissolves the mostly lipophilic extractives of the stone pine heartwood, favoring the penetration of the preservative solution [19].  
The uptake of Belocid in the sapwood of Scots pine and stone pine with the vacuum method was not statistically different (240.28 \(\pm\) 25.55 kg/m\({}^{3}\) in Scots pine and 314.40 \(\pm\) 9.97 kg/m\({}^{3}\) in stone pine). The same result was observed with the full-cell method because no statistically significant difference was found between the sapwood of Scots pine (418.09 \(\pm\) 7.7 kg/m\({}^{3}\)) and of stone pine (393.88 \(\pm\) 51.42 kg/m\({}^{3}\)).  
The uptake of water-based Silvanolin (516.91 \(\pm\) 45.74 kg/m\({}^{3}\)) was not statistically different from the uptake measured in Scots pine (590.34 \(\pm\) 11.99 kg/m\({}^{3}\)) in sapwood tissue.  
Uptake also depends on the chemical agents used for impregnation; however, as the active ingredients are dissolved in the water or in an organic solvent, this does not significantly affect penetration. Samples impregnated with the full-cell method showed the lowest uptake of the preservative solution when Belocid was tested for almost all woodspecies. Looking at Italian stone pine sapwood and comparing the different tested preservative products, the statistically significant lower uptake compared to the one of Scots pine was found in samples treated with Montax 50 and full-cell method (450.53 \(\pm\) 52.36 kg/m\({}^{3}\) with stone pine sapwood and 565.25 \(\pm\) 8.55 kg/m\({}^{3}\) with Scots pine sapwood). This clearly shows that the permeability of the two pine species using vacuum and full-cell method was comparable except for the samples treated with Montax 50, which showed a better penetration in Scots pine.