< ALTERNATIVE PROTECTIVE COATINGS
GILDING
The gilding of cast and other metal designs involves the application of a fine metal foil, usually gold, silver, platinum, copper or other metal/alloy. Gilding metal is first worked (beaten) to achieve a thickness as fine as 0.0001mm, with the resulting product normally supplied in the form of a loose BOOK, or else as a TRANSFER LEAF backed onto a grease proof paper. In either case the leaf supplied is cut to regular squares of 4 inch sides, made up to an individual book weight of 3.1g nett (1/10 troy oz).
Traditionally, gilding is practiced using one of two basic techniques. The first and best known gilding process involves the direct application of a foil or leaf to the cast. Before application commences, the cast’s surface is prepared specifically for the leaf. This normally includes degreasing the metal and applying a sealant or PRIMER coating. The primer helps prevent any adverse interaction between the dissimilar metallic compositions of the cast alloy and the leaf. An adhesive GROUND or SIZE is then be applied over the primer and permitted to partially dry. Adhesive sizes with various drying times are available, some of up to twenty four hours or more, offering the gilder a choice of convenient working times for leaf application (note, an oil based size must be used if the finished artwork is intended for out of doors display).
Leaf is applied to the surface of the cast when the size becomes ‘tacky’. The leaf is lifted from the book with an electro-static charged brush technique (loose-leaf foils), or alternatively, by manually applying a leaf still mounted on it’s non-adhesive backing paper (transfer leaf). The procedure is repeated, slightly overlapping each adjoining leaf edge, and carefully brushing out any trapped air between the leaf and the cast, until the sculpture is covered. After the sized ground has dried and hardened the leaf can be BURNISHED, then given protective lacquer or varnish finish. Unlike heavier, more opaque finishes, the exceptionally fine thickness of leaf often permits the underlying metal surface (or else an enhanced colour ground), to reflect light back through the deposited leaf layer, improving the visual quality of the leaf. This light reflective effect is somewhat diminished if more than one layer of leaf is applied, as is often the case if surface durability and longevity is a paramount consideration.
The second method of gilding a cast surface depends upon the ability of gold to be dispersed within a mercuric preparation to form an AMALGAM. The fluid amalgam is then applied direct to the cast’s surface. After the amalgam has been deposited excess mercury is driven off by ambient evaporation or heating, to leave a fine residue of fixed gold over the treated surface.
This traditional technique, also known as FIRE GILDING or ORMOLOU (from the French term ‘Doré d’or Moulu’), was especially prominent throughout the Italian Renaissance - though it was widely practiced prior to the period. The ‘Horses of San Marco’, the celebrated Venetian trophy acquired from the conquest of Constantinople in 1204, are among the best known examples of fire gilded sculpture [ref]. A rather more intact example is the late 15th/early 16th century standing Buddah from Ayutthaya (Thailand), this work can be viewed within the SE Asian gallery at the Victoria & Albert Museum, London.
The health hazards associated with the handling of mercuric compounds, and in particular, the potential for exposure to toxic vapours evolved when ‘burning off’ an amalgam, means that fire gilding can no longer be considered a viable method of finishing artwork. As such, the technique of fire gilding is these days effectively redundant.
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