Gilding: manufacturing and processes

Gold is one of the first metals to have been shaped by man, as it exists in its native state; its great ductility means that it can be plastically deformed using very basic means. It was first used to make ornamental, cultural and even cultic objects, as early as the 5th millennium, but the idea soon arose of using this inalterable, extremely ductile and precious metal to sublimate the material by coating it, giving it a luxurious and divine character at a lower cost.

This article is devoted to gilding, i.e. the process of obtaining a gilded surface on objects or works of art by applying a foil, treatment or coating. The first part outlines the main stages in the appearance and historical development of these processes. Leaf gilding, the first to appear as early as High Antiquity, very soon required the development and refinement of a very elaborate technique, beating, the mechanical aspects of which are modeled and discussed here. This is followed by a detailed description of the technological stages of the processes that developed after leaf gilding: gilding by diffusion, mercury amalgam, surface depletion and electrochemical methods. Other processes, applied to many different substrates, are described, such as powder gilding, and much more recently, liquid gold gilding and gilding by physical vacuum deposition, not forgetting to mention the recipes commonly developed for false gilding. The still evolving subject of knowledge of the physico-chemical and mechanical properties of the gold-substrate interface is discussed: variety and properties of adhesives in leaf gilding, modes of adhesion in other types of gilding. Finally, aspects of gilding degradation and restoration are discussed.