## 3 Results and Discussion
### Filler and Coatings Aspect
However, the wax-based additive also affects the texture of the coating, in addition to its color. The bio-based powder leads to an important reduction in gloss values, as illustrated in the graph in Figure 3a, indicating a pronounced opacity of the coating. Indeed, even a 5 wt.% addition of the powder is sufficient to reduce the gloss values of the paint from 50 to 20. This reduction is further pronounced, albeit not linearly, by doubling the quantity of _green_ additive. Once again, the UV absorber demonstrates no impact on the aesthetics of the coating, without influencing the behavior of the wax-based filler. However, as reflectance values of a surface are often closely linked to its roughness values, the samples underwent surface roughness measurements to discern whether the varied gloss values are attributed solely to the presence of wax or to different surface textures. Figure 3b exhibits the results of these analyses. Considering that paint tends to conform to the surface morphology of the substrate upon which it is applied, the measurements were carried out both parallel (Ra//) and perpendicular (Ra\(\perp\)) to the fibers of the wooden substrate, anticipating distinctly different outcomes. Indeed, the Ra\(\perp\) values are significantly higher than those of Ra//, mainly due to the influence of the wooden panel's morphology. However, simultaneously, all four series of samples display roughness values that are comparable to each other, indicating that the bio-based additive does not impact the surface morphology of the composite layer. This finding further confirms that the variations in gloss values shown in Figure 3a are not a result of differing roughness in the coatings but are solely attributed to the presence of the wax-based additive, which demonstrates noticeable matting capability. Similarly, analogous behaviors have been previously observed in the literature concerning wax-based fillers [32; 34]. Ultimately, the influence of the additives on the structure of the coating was assessed by examining the cross-section of the samples under SEM, following a brittle fracture process carried out in liquid nitrogen. The images in Figure 4 illustrate an example of the internal structure with a cross-section view of the four sets of samples, emphasizing the  
Figure 3: (**a**) Glass measurements of the four series of samples and (**b**) surface roughness of the coatings in parallel (Ra//) and perpendicular (Ra\(\perp\)) orientations. bulk morphology of the coating. As previously described, the coatings in the four sets of samples have comparable thicknesses, approximately 100 \(\upmu\)m. Consequently, both the wax powder and the UV absorber additives do not influence the deposition process or alter the rheological properties of the paint. On the other hand, the SEM observations highlight that the addition of the wax-based powder produces a progressive structural modification of the layer, where the bulk appears significantly more intricate due to the presence of various extraneous bodies such as the granules of the _green_ additive. Sample G10 in Figure 4c, in fact, demonstrates how the brittle fracture process leads to the release of many of these granules, resulting in a fracture surface that is not linear, akin to sample G0 (Figure 4a), but notably jagged. This phenomenon underscores and emphasizes that substantial amounts of additives can notably modify the internal structure of the coating. This aspect can be critical in some cases, leading, for example, to enhanced absorption of aggressive ions and diminished barrier properties of the composite layer due to a weak interface between the matrix and additive. Consequently, these features will be duly considered in subsequent tests pertaining to the barrier performance of the four series of coatings. In conclusion, the bio-based additive demonstrates commendable coloring power, thereby serving as an eco-sustainable pigment.