Does substrate colour affect the visual appearance of gilded medieval sculptures? Part I: colorimetry and interferometric microscopy of gilded models

Abstract

In the history of medieval gilding, a common view has been circulated for centuries that the substrate colour can influence the visual appearance of a gilded surface. In order to fully understand the correlation between the gilding substrate and the colour appearance of the gold leaf laid above, in this paper (Part I) analytical techniques such as colorimetry and interferometric microscopy are implemented on models made from modern gold leaves. This study demonstrates that the substrate colour is not perceptible for gold leaf of at least 100 nm thickness, however the surface burnishing can greatly alter the visual appearance of a gold surface, and the quality of the burnishing is dependent on the substrate materials. Additionally, surface roughness and texture of the substrate can play supplementary roles, which can be visually observed through digital microscopy and quantified through interferometric microscopy. The findings in this paper will form the basis for the study of gold leaf samples taken from medieval European gilded sculptures in Part II.

Appearance-based evaluation of varnish removal methods in gilded surfaces

“…Wu et al [15] study the influence of substrate colour on the visual appearance of gilding. Gilding mock-ups were fabricated using different methods such as oil gilding, water gilding, and ground gilding.…”

“…However, the focus is on the imaging device's advantages and limitations, as well as the spatial and spectral quality of the data, not the appearance of the gilding. In the case of evaluating the appearance of gilded surfaces more specifically [3,15,32,33], studies are limited to colorimetric measurements which are not sufficient to describe the complete visual appearance of gilding. Moreover, these do not evaluate the effect of removing varnish from gilded surfaces.…”

“…Recommendations by experts and industry are to perform psychophysical experiments to define gloss tolerances for a batch of samples [14]. In the case of gilded surfaces, many factors can affect their visual perception such as the illumination type, geometry and intensity, the viewing conditions, the material composition of the gilding, and the presence of surface coatings, to name a few [15].…”

Appearance-based evaluation of varnish removal methods in gilded surfaces

“…However, the focus is on the imaging device's advantages and limitations, as well as the spatial and spectral quality of the data, not the appearance of the gilding. In the case of evaluating the appearance of gilded surfaces more specifically [18,19,4], studies are limited to colorimetric measurements which are not sufficient to describe the complete visual appearance of gilding. Moreover, these do not evaluate the effect of varnish on gilded surfaces.…”

“…Recommendations by experts and industry are to perform psychophysical experiments to define gloss tolerances for a batch of samples [3]. In the case of gilded surfaces many factors can affect its visual perception such as the illumination type, geometry, and intensity, the viewing conditions, the material composition of the gilding, and the presence of surface coatings, to name a few [4].…”