Non-traditional gilding revisited: evaluation of gilded surfaces exposed to uncontrolled diurnal fluctuations for over 10 years

Options for loss compensation in water-gilded objects are limited by a constrained number of materials and techniques suitable to imitate distinctive appearance of gilding and a conservators’ individual preference for traditional or non-traditional methods. Evidence-based assessments of selected conservation materials indicated that the synthetic materials, acrylic dispersion Plextol B500, acrylic resin Paraloid B-72, and polyvinyl acetate resin AYAF, are potentially the most useful for compensation of losses in matte water-gilded objects. This prompted a series of experiments involving the testing of ageing characteristics of three synthetic polymers used in gilding, in comparison to those used in traditional gilding. A frame sample, which was gilded using both traditional and non-traditional techniques, was exposed to diurnal fluctuation in relative humidity (RH) and temperature through window glass without ultraviolet filtering for over 10 years. Subsequent examination of the gilded surfaces suggested that fluctuations in humidity occurring in diurnal cycles were inadequate to trigger any failure to gilding caused by movement of the wooden substrate; and any damage to gilding was a consequence of changes affecting the surface only of a protective layer, gold leaf, and polymers. The experiment showed that substantial temperature/humidity fluctuations can cause significant stress, particularly for Paraloid B-72 resin. Furthermore, this experiment demonstrates that Paraloid B-72 resin developed greater brittleness with age than either AYAF or Plextol B500. Despite the obvious physical changes evident within the polymer films, there were little alterations observed in their Fourier transform infrared spectra.