Foil and leaf gilding on cultural artifacts: forming and adhesion

Abstract

The process used to obtain foils of more and more thin thickness and coat them on artefacts varied during centuries. It started from thick foils of the first ages mechanically assembled and evolved until the rolled and beaten leaves, a few hundred nanometres thick. This paper will develop, through examples taken from laboratory studies on museum objects, the main evolution steps of gold leaf forming. It will discuss the present knowledge about processes used by hand-workers of different origins and periods: antic Egypt, Roman Empire, western and oriental Middle-Age, South America, modern Europe. A recent mechanical modelling work about gold forming by beating will be exposed. Then will be described, still through recent examples, some of the non-destructive and destructive laboratory methods used to characterise ancient and modern gildings, their composition, thickness and adhesion modes. The different coating process will be discussed, owing to the presently available knowledge. These depend on the substrate nature and the possible necessity to treat its surface before and during the gilding process. Such treatment varies from the "white preparation" found on antic Egyptian artefacts and also on wooden decoration of baroque Brazilian churches, to "oil gilding" used for the recent restoration of the Invalides roof in Paris. It may also include a high temperature firing, as for gilding with powder issued from leaf grinding on Middle-Age Syria glass. The paper will end with a listing of the numerous research perspectives open for the presently poorly developed study of the adhesion mechanisms between gold leaf and its substrate, to understand fully the gilding process.Keywords: Cultural heritage, Gilding, Surface, Adhesion, Forming INTRODUCTIONGold foil and leaf have been used by most human civilisations to decorate all kinds of artworks: bronze, stone, ceramic, wood, cartonnage of the Egyptian sarcophagi, glass objects, etc. The present paper is an attempt to draw a summarised story of the gold foil and leaf preparation and coating on various materials used in cultural heritage artefacts along the ages, starting from the thick gold foils mechanically fastened onto metal or ceramic pieces of ancient Egypt or Mesopotamia to reach the very thin gold leaves applied on the surface of precious wood sculptures during the Baroque period or on the metallic roof of the Invalid Church in Paris. That crucial question of the mode of thinning of the gold leaves will be discussed from the mechanical viewpoint and a model will be developed explaining how the exceptional mechanical properties of gold allow obtaining metal leaves of an extreme thinness, a specific process refined by generations of gold hand workers and still used at the present time.But foil or leaf gilding is not only a question of obtaining good quality and colour gold films; it is also a process of coating which was applied to a very large number of substrate materials. This required from the artisans the invention of various kinds of recipes to obtain ...

Tracing the 5000-year recorded history of inorganic thin films from ∼3000 BC to the early 1900s AD

“…17,31 Sheathing is the direct application of thin gold layers onto wooden and plaster objects (mostly for noble families) to give the impression that the object is solid gold. Striking examples were found in the tomb of Queen Hetepheres (wife, and half-sister, of Pharaoh Sneferu, Fourth Dynasty, Old Kingdom, $2613-2589 BC).…”

In situ scanning micro-XRF analyses of gilded bronze figurines at the National Museum of Damascus

“…32 There are no visible grooves on the examined objects, suggesting that the foils were mechanically fastened through the hammering process 19 and possibly by crimping. There have been studies 19,20,22 that report the technique of inserting a mineral layer, oen called "white preparation" made of calcite or plaster (gypsum) between the substrate and the gold leaf. There have been studies 19,20,22 that report the technique of inserting a mineral layer, oen called "white preparation" made of calcite or plaster (gypsum) between the substrate and the gold leaf.…”

“…15 At that period, Ugarit became the center of interaction between Egypt, Crete, Cyprus and Anatolia promoting the exchange of the rst artistic styles within the ancient world. [18][19][20][21][22][23] Foil gilding was common in Mesopotamia with a mechanical or physical (pressed) application of a layer of gold onto the surface of a less precious metal. In the El God gurine (Fig.…”

Preliminary investigation of the materials and techniques used in a decorated wooden stick of king Tutankhamun

“…In addition, dirt adhered to the varnish layer was also observed as a fourth layer. It was a common practice to use gold leaf on a white ground layer for the decoration of furniture in ancient Egypt, in particular in the New Kingdom, and this technique was reported by some authors [15,[18][19][20].…”