Physicochemical degradation of historical wax seals: chemical composition and microstructural analysis

A significant proportion of historical wax seals is susceptible to a specific type of degradation, characterised by opacity, a porous structure, and unusual brittleness. Based on the indirect evidence presented, it was suggested that the formation of a primary layered structure might result from the kneading of unrefined raw material prior to the sealing process itself. It was further hypothesised that the surface-to-mass ratio of the material was the determining factor for the rate of the subsequent physicochemical degradation processes. These processes were studied on pairs of well-preserved and degraded historical wax samples, obtained from the same seals. The results of a comparative analysis indicated that the differences in chemical composition could be attributed to a combination of oxidative and hydrolytic reactions, accompanied by the volatilisation of low molecular weight components. These findings confirmed that the condition of affected wax seals could not be considered stable in the long term.