## 2 Materials and Methods
### Methods  
#### 2.2.1 Impregnation with Preservative Solutions  
Seventy-five samples of sapwood and 15 of heartwood were cut with a size of \(25\times 25\) mm in cross-section and 100 mm in length for the tests of impregnation of the wood with preservatives. The cross-sections of the samples were sealed with a double layer of epoxy resin to allow penetration of the solution only in the radial and tangential directions. An equal number of sapwood samples of Scots pine, Norway spruce, and beech wood were used as controls and prepared in the same manner. Spruce was selected as the control because it is known that the species when dried under 30% moisture content is refractory to impregnation because of the aspirated pits in the tracheid [23; 24; 25]. Five samples were used for each treatment and preservation product. Before treatment, the samples were conditioned at 20 \(\pm\) 2 \({}^{\circ}\)C and 65 \(\pm\) 5% relative humidity, and the mass was determined. The standard EN 351-1:2008 [26] was used to investigate the impregnability of the wood with wood preservatives. Three different impregnation methods were used: (I) vacuum impregnation, (II) full-cell pressure method, and (III) soaking. Three soaking method impregnation durations were applied: 15, 60, and 480 min. As the low permeability of the heartwood was to be expected and due to the limited quantities of heartwood, the stone pine heartwood was treated only with the full-cell method, which is one of the most commercially important methods. The amount of preservative absorbed was measured by gravimetric analysis, taking into account the difference in density. Samples were placed in plastic containers and soaked with the preservative for each treatment. An inert mesh of polyethene terephthalate (PET) with a mesh size of 10 \(\times\) 10 mm was used to separate the samples. Lead weights were used to prevent the samples from floating. The treatments were carried out at room temperature. A laboratory-scale impregnation chamber (Kambic, Semic, Slovenia) was used for vacuum and full-cell treatment. Vacuum (\(-\)0.085 MPa) was applied for 30 min, and then the samples were submerged at atmospheric pressure for 2 h. For the full-cell treatment, the samples were first kept under vacuum (\(-\)0.085 MPa) for 20 min, then under high pressure (1 MPa) for 2.5 h, and finally under vacuum (\(-\)0.085 MPa) for 30 min. The specimens were left for an additional two hours and immersed at atmospheric pressure to determine as much accurate retention as possible as prescribed from the leaching standard ENV 1250-2:1994 [27]. At the end of each treatment, the samples were carefully wiped to remove the excess preservative and weighed to the nearest 0.01 g. Radial and tangential penetration of Silvanolin was checked by cutting the samples along the midsection and treating them with a 2% potassium ferrocyanide reagent. The presence of Silvanolin was highlighted by the reagent with a dark reddish color. The depth of penetration was measured for each sample at the middle point of each of the four sides of the section. The experiment was carried out in five replicates. Unfortunately, we could not determine the penetration of Montax 50 and Belocid because these preservative solutions are colorless, and no color reagents have been developed to make their penetration visible.