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

Qing Wu,Meret Hauldenschild,Benjamin Watts,Frithjof Nolting,Benedikt Rösner,Tiziana Lombardo,Katharina Schmidt-Ott,David Ganz

doi:10.1186/s40494-020-00463-3

Qing Wu, Meret Hauldenschild + Show 6 more

Open Access

https://doi.org/10.1186/s40494-020-00463-3

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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.

Highlights

As the climax epoch for altars and altar sculptures, the late Middle Ages exhibited exquisite art technologies and complex materials in the sculpting, carving and polychromy of these artefacts
We focus on understanding the correlation between the appearance of the gold leaf and its substrate through colorimetry measurements on the models, which are made with traditional gilding techniques including water, oil- and ground gilding on substrates with different materials and colours
Measurements on gold surfaces with different apertures During the colour measurements on gold surface of models, it is observed that the Specular Component Included’ (SCI) values of ∆E*ab for almost all “nb” and “b” sub-models are below Just Noticeable Difference (JND), which is inconsistent with our visual perception that the burnished gold surface appears darker and more saturated than the unburnished one

Summary

Introduction

As the climax epoch for altars and altar sculptures, the late Middle Ages exhibited exquisite art technologies and complex materials in the sculpting, carving and polychromy of these artefacts. One widely accepted point of view states that the colour of the gilding substrate plays a crucial role in the visual appearance or perception of medieval gilded artefacts due to the transparency of the gold leaf of that time [2] This view sounds plausible and has sometimes been used to explain why certain substrate colours such as red, yellow and white have been frequently observed in medieval gilding. Before the water and oil gilding techniques became popular in European works of art, a variant of water gilding called ground gilding was the main gilding type prior to the mid thirteenth century [2, 5] In this technique, metal leaf is applied onto a polished ground by means of thin adhesives such as diluted animal glue or egg glair [5, 11], and can be slightly burnished [9]

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