## Materials and Methods
### Research Setup  
Four sets of four thermosetting resin samples (diameter: 5.5 cm/thickness: 3.65 mm \(\pm\) 0.3 mm) were fabricated and enriched with ZnO (nano)particles at 4 percentages: bare 0 wt% (C0), 0.1 wt% (C0.1), 0.5 wt% (C0.5) and 2 wt% (C2). An additional sample of every concentration was fabricated and kept untreated, serving as control samples. DSC measurements (Mettler Toledo DSC 1) pinpointed the glass transition temperature and thus, the suitability of the selected resin as a protecting agent.  
The samples were exposed to an Artificial Weathering Environment (AWE) (QUV/Spray with UVB-313 EL lamps) for a total period of 2880 h. Treatment was based on 4-h interchanging UV radiation cycles (0.68 W/m\({}^{2}\) at 45 \({}^{\circ}\)C) and condensation cycles (100% RH at 40 \({}^{\circ}\)C). In that manner, the full experimental procedure comprised 5 sets of 576-h AWE treatment intervals, between which measurements took place.  
The morphology of ZnO powder and its dispersion were examined by SEM (ThermoFischer Scientific Phenom XL G2). Optical microscopy outlined surface damage of all samples (Leitz Aristomet). X-Ray crystallography (Bruker D8 Advance with CuK\(\alpha\) radiation, 40 KV, 40 mA at an increment step of 0.040\({}^{\circ}\)/min, \(\lambda\) = 0.154 nm) was performed for determining filler crystallinity. Surface degradation was evaluated by glossimetry (Sheen Tri-Microgloss 20-60-85). Contact angle (Rame-hart 590/DROPimage Advanced) established surface wettability. Gravimetric measurements determined sample weight loss (WL) and sorbed moisture (SM) inside sample bodies. Specifically, all samples were placed inside a controlled humidity chamber (100% RH/40 \({}^{\circ}\)C) for a period of 168 h. Then, they were carefully washed with jets of distilled water and left to dry in a protected enclosure under ambient conditions (temperature 28 \(\pm\) 2 \({}^{\circ}\)C, RH 30 \(\pm\) 5%) for a period of 24 h, until the SM inside them reached equilibrium concentration. This sample state has been designated as the humid state (HS). As a next step, samples were reconditioned by means of vacuum-drying for a period of 168 h at 0.1 mbar/28 \(\pm\) 2 \({}^{\circ}\)C. This condition has been designated as the dried state (DS). Moisture content was then calculated by gravimetric comparison of samples between HS and DS, with the use of analytical balance (Ohaus Galaxy 110, 0.1 mg precision). Next, 2880 h aged samples were exposed to a further 1000 h time period under 40 \({}^{\circ}\)C/100% RH environment, so as to determine the saturation moisture content. UV-Vis spectroscopy (Jasco V-770) was performed at a wavelength range of 300-850 nm. FTIR measurements (Jasco FT/IR 4200) were performed at a wavenumber range of 4000-400 cm\({}^{-1}\) using KBr tablets containing a portion of sample surfaces. Additionally, sample surfaces were assessed by means of colorimetry measurements in CIELAB colour space (Sheen Micromatch Plus), where parameter L\({}^{\star}\) quantifies/stands for the brightness levels in a range of 0-100 (0: darkest, 100: brightest), parameter a\({}^{\star}\) quantifies/stands for greenness when a\({}^{\star}\) < 0 and redness when a\({}^{\star}\) > 0 and parameter b\({}^{\star}\) quantifies/stands for blueness when b < 0 and yellowish when b\({}^{\star}\) > 0 [33]. Dielectric spectroscopy (Agilent 4287A) was studied in the VHF and a portion of the UHF frequency spectrum.  
Measurements were performed under virtually the same ambient conditions (28 \(\pm\) 2 \({}^{\circ}\)C/RH 30 \(\pm\) 5%); additionally, throughout the entire experiment, all samples were kept in protected cases to avoid contamination by volatile content, and they were handled carefully, preventing all tactile contact. Finally, the experiment was designed to not impose any further strain (mechanical, chemical, etc.) on the samples, other than the AWE treatment.