## 2 Materials and Methods  
The raw material of this experimental work consisted of logs of five European hardwood species of Greek and Balkan origin of large diameter (350 mm mean diameter). Specifically, one log was examined per examined forest species, which were oak (_Quercus robur_ L.), chestnut (_Castane sativa_), ash (_Fraxinus excelsior_ L.), hybrid poplar (_Populous_ spp.) and wild cherry (_Prunus avium_). Only the poplar wood was of Greek origin, while the rest of the species used were obtained from 3 different Balkan countries (Romania, Croatia and Serbia), and they were all commercially converted into decorative sliced veneer sheets, using the veneer slicing method, applied in the infrastructures of a Greek industry of sliced veneer production, located in central Greece (Chalkida, Evia), so that the processing conditions, the cutting means and the slicing method applied would be common for the five wood species. The veneer production fulfilled the requirements of the industrial sliced veneer production standards of this certified company, as regards the absence of thickness inequalities, defects attributed to mechanical processing failures, like burning, etc. The trunks were initially peeled to remove the bark, cut into logs, and then steamed under the same conditions (duration, temperature, pressure) followed by the industry, prior to the slicing process. The cutting machine used for the slicing of veneers was of horizontal operation, since this is suitable for the veneer slicing of hardwood species and they were all cut into plain cut (flat cut) veneers. After a visual assessment of the defects on the produced veneers, for each case of wood species and defect species, a package of 10 sliced veneer sheets, continuous in a row and successively cut, was obtained, aiming to observe the evolution of the whole defect as it is encountered in the trunk mass. The veneer sheets produced were of \(0.55\pm 0.1\) mm thickness, mainly cut from the heartwood part of trunks and for the purposes of this experiment, they were cut in our laboratory in smaller dimensions (350 mm length \(\times\) 250 mm width) to be easily handled, and were left to be conditioned at \(20\pm 2\)\({}^{\circ}\)C and \(65\pm 5\%\) relative humidity, until constant weight. All veneer samples were conditioned to equilibrium moisture content (EMC), which ranged at low levels (5.5-10%) [14]. Twenty days before the roughness measurements' implementation, the veneers were anchored tightly on flat surfaces and, subsequently, the veneer sheets' surfaces were slightly sanded with 80-grit sand paper for 15 s. under the same laboratory conditions, since the sanding process creates a new and fresh surface by removing the material and, therefore, can improve the surface quality of veneers before finishing [15]. Afterwards, the veneers were removed from the abovementioned flat surfaces and left for approximately three weeks to be conditioned at \(20\pm 2\)\({}^{\circ}\)C and \(65\pm 5\%\) relative humidity, until constant weight. At the end of the conditioning duration, the EMC was measured again by applying the drying method of the veneer samples [14] and recording similar EMC values with those prior to the sanding and conditioning processes (\(<\)10%). The mean density of the veneers was also measured after their conditioning process (calculated as dry mass/wet volume, with volume measured in the state of the EMC), following the respective international standard process [16], with the only difference that specimens of different dimensions were measured (20 mm \(\times\) 20 mm \(\times\) 0.5 mm). For the dry mass measurement, a weight of high accuracy (of 4 decimals) was used, and for the volume determination, a digital caliper was used. The density of oak wood was found to be 0.742 g/cm\({}^{3}\), of chestnut wood was 0.554 g/cm\({}^{3}\), of ash wood was 0.705 g/cm\({}^{3}\), of poplar wood was 0.385 g/cm\({}^{3}\) and of cherry wood was 0.627 g/cm\({}^{3}\).