## 3 Results and Discussion
### Light-Induced Colour Changes in the Coated Wood Surfaces
Comparing the F values of the two factors, it results that wood species (F = 52.72) influence more the colour changes than the type of coating (F = 15.29). The test shows also that there is a significant two-way interaction between the two factors (\(p\) < 0.05; F = 3.31). This would mean a common and interconnected influence of the two factors for each wood species and type of coating. A significant impact of wood species and type of lacquer/coating system, alongside pre-treatments of wood surfaces and modification of coatings, on the light-induced colour changes in wood surfaces was previously reported [59]. The interaction of the coating material with the wood substrate at the interface level, consisting in wetting and penetration, depending on both the structural features and surface properties of the substrate and the coating material, might be part of this significant two-way influence on the UV-induced colour changes determined in this research. According to the literature data, a combination of the wood anatomy and the ability of the coatings to flow into the wood capillaries, influenced by the viscosity, solids content and type of solvent, govern the degree of coating penetration [60]. Generally, waterborne coatings penetrate less than the solvent-borne ones, though large variations might be among different formulations. In this context, binder type, pigmentation, solids content and drying time were found to be important. Acrylic waterborne dispersions have been found to have a low penetration compared to alkyl emulsions [61; 62]. Differences in the colour changes in clear-coated pine wood after an artificial weathering test were associated with different penetrations of an acrylic coating system (primer and topcoat), increased colour changes being explained as possibly due to a reduced coating penetration. Increased penetrations were obtained in the same research for beech wood, but no final conclusion was drawn on the influence of coating penetration on the colour changes caused by weathering [63]. An interesting study on the degradative behaviour of coated-wood surfaces exposed to artificial weathering using Raman microspectroscopy was recently published. Chemical imaging pointed out different artificial weathering degradation patterns between wood specimens (Japanese cedar) that were clear-coated with impregnating materials and film-forming materials. For the impregnating systems, the surface-distributed coating gradually decreased during irradiation and lignin in the top surface cell walls degraded similarly to \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Anova: Two-Factor with Replication (\(\alpha\) = 0.05)** & & & & \\ \hline
**Source of Variation** & **SS** & **df** & **MS** & **F** & \(p\)**-Value** & **F Crit** \\ \hline Wood species (1) & 266.8111 & 2 & 133.4055 & 52.71715 & 3.83802 \(\times\) 10\({}^{-18}\) & 3.055162 \\ Type of coating (2) & 77.40668 & 2 & 38.70334 & 15.29419 & 8.80515 \(\times\) 10\({}^{-7}\) & 3.055162 \\ Interaction (1)x(2) & 33.53909 & 4 & 8.384773 & 3.313366 & 0.01233886 & 2.430772 \\ Within & 387.1804 & 153 & 2.530591 & & & \\ Total & 764.9372 & 161 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of two-way Anova results with replication of the colour change (\(\Delta\)E, after 72 h light exposure) in the coated wood surfaces (areas V2/Z1), considering the wood species (1) and the type of coating (2) as influencing factors. uncoated wood [64]. The result is, therefore, that both good penetration and the formation of a top film of the coating are beneficial for improved UV protection. The preliminary microscopic investigation of our samples highlighted such \"composite coating layers\" with total thicknesses varying in the range of approximately 25-75 \(\upmu\)m, while the top layer film included varied in the range 5-20 \(\upmu\)m, with maximum thickness in ash early-wood (vessels).