The mechanical and chemical finishing of gilt bronze ornaments and mountings was a complex and delicate balance of glossy and matted surfaces of different hues, that peaked during the 18th and 19th century in Paris. Although many...
moreThe mechanical and chemical finishing of gilt bronze ornaments and mountings was a complex and delicate balance of glossy and matted surfaces of different hues, that peaked during the 18th and 19th century in Paris. Although many contemporary sources at least give an idea of the operations and ingredients involved, the exact recipes seem to have been kept secret. Matthew Boulton for example, in trying to compete with the French workmen, noted in the 1760’s:
[I wonder] how and with what ingredients the French gilders colour their fine gilt sconces after they are gilt, for I observe that most of them gild upon brass instead of pinchbeck which gilding upon brass will always be paler than that upon pinchbeck, yet nevertheless their sconces when finished appear of deep golden orange red and therefore I presume they are boyled in some sauce or other after they are gilt. (Goodison: The work of Matthew Boulton,1974, p 73)
The knowledge of the chemistry of these “sauces” developed during the early 19th century and even further today. Apart from recipes that are based on dyes in waxes, most actually seem capable of altering the composition of the surface by diffusion of metals and metal oxides into the gold. Traces of these coloring treatments might still be present today.
In this paper, the main types of recipes will be discussed, their development, chemistry and coloring effect and the consequences for conservators that treat these objects.
