## 4 Discussion  
In terms of application efficiency, fillers M3 and M9 demonstrated excellent workability, ease of handling, and adequate surface adaptation, making them particularly suitable for on-site interventions. M3 also recorded the highest gloss level (>110 GU), indicative of a well-suited surface for burnished gilding. M9 combined this ease of application with stability during drying and good abrasion resistance. In contrast, M6 and M9 exhibited greater complexity in the preparation phase. Although inferential statistics were not applied due to the limited sample size, the data provide robust comparative trends that support material selection in conservation practice.  
The evaluation of compatibility with the water gilding technique considered both optical performance and abrasion resistance. Formulations M2, M4, M8, and M9 performed remarkably well, limiting losses to the gold leaf while preserving the bole and base material, especially under burnished gilding conditions. M3 maintained acceptable performance even after the fourth cycle, whereas M1, despite its good internal cohesion, was among the most affected by abrasion, suggesting surface vulnerability under frictional stress.  
Figure 14: ATR-FTIR spectra of two filler materials (**left**: M1; **right**: M9) across the aging cycles. The graphs show changes in absorbance as a function of wavenumber (cm\({}^{-1}\)), highlighting the decrease in intensity of the O-H stretching band (3300–3400 cm\({}^{-1}\)) and other relevant functional group regions over time. Source: Authors’ own elaboration, Dor.ART Project, 2025.  
Regarding mechanical stability, tensile strength testing showed that M1 and M4 achieved their highest strength values (13 MPa) in the second cycle. Most formulations reached their peak strength during that cycle and then progressively declined, likely due to aging effects. M3, however, displayed different behavior: after an initial decrease, it recovered strength by the fourth cycle, indicating potential long-term stabilization. M5, although showing low strength values, displayed a slight progressive improvement.  
In terms of adhesion to the wood support, M1 stood out with an initial value of 8.23 MPa and good performance over time. M2 showed high initial adhesion but suffered a progressive loss of internal cohesion.  
Shore C hardness measurements revealed that M1, M4, M5, M7, and M9 presented the highest values (90-95 HC), while M2 and M6 had the lowest values. For some of the putties studied, such as M2, M3, and M8, their hardness increased after aging, suggesting internal crosslinking processes, while M4, M5, and M6 showed significant reductions in hardness, indicating possible degradation of their matrices.  
Chemical-structural analysis using ATR-FTIR revealed a general reduction in -OH groups due to dehydration induced by thermo-hygrometric aging conditions. However, in M1 and M9, possible partial regeneration of these groups was observed, attributed to mild oxidation or exposure of previously inaccessible functional groups. The oxirane ring band (\(\sim\)910 cm\({}^{-1}\)), present in materials with epoxy components, was suggestive of curing reactions or the loss of unreacted epoxide groups, particularly in M1. Carbonyl-related bands (\(\sim\)1730 cm\({}^{-1}\)) increased slightly in M1, M4, and M9, suggesting the onset of oxidative processes. In materials with inorganic components (M5, M6, M8), variations were detected in the 1100-900 cm\({}^{-1}\) region, related to internal reorganization of sulfate or silicate phases. In contrast, M3, M7, and M9 showed minimal spectral changes, suggesting greater chemical stability during the aging process.  
Overall, the data obtained indicate that formulations M3 and M9 offer a particularly favorable balance between application efficiency, compatibility with the water-based gilding technique, and mechanical and chemical stability on gilded wooden heritage objects.