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Gilding is a decorative technique for applying a very thin coating of gold over solid surfaces such as metal (most common), wood, porcelain, or stone. A gilded object is also described as "gilt". Where metal is gilded, the metal below was traditionally silver in the West, to make silver-gilt (or vermeil) objects, but gilt-bronze is commonly used in China, and also called ormolu if it is Western. Methods of gilding include hand application and gluing, typically of gold leaf, chemical gilding, and electroplating, the last also called gold plating.Sloan, Annie (1996) Decorative Gilding, Collins & Brown, Parcel-gilt (partial gilt) objects are only gilded over part of their surfaces. This may mean that all of the inside, and none of the outside, of a chalice or similar vessel is gilded, or that patterns or images are made up by using a combination of gilt and ungilted areas.
Gilding gives an object a gold appearance at a fraction of the cost of creating a solid gold object. In addition, a solid gold piece would often be too soft or too heavy for practical use. A gilt surface also does not tarnish as silver does.
Modern gilding is applied to numerous and diverse surfaces and by various processes. More traditional techniques still form an important part of Picture frame and are sometimes still employed in general woodworking, cabinet-work, decorative painting and interior decoration, bookbinding, and ornamental leather work, and in the decoration of pottery, porcelain, and glass.
Pliny the Elder recorded that the first gilding seen at Rome was after the destruction of Carthage, under the censorship of Lucius Mummius, when the Romans began to gild the ceilings of their temples and palaces, the Capitoline Hill being the first place where this process was used. Gilding became a popular luxury within Rome soon after the introduction of the technique, with gilding soon being seen used on the walls, vaults and inside the houses of anyone who could afford it, including the poor. Owing to the comparative thickness of the gold leaf used in ancient gilding, the traces of it that remain are remarkably brilliant and solid. Fire-gilding of metal goes back at least to the 4th century BC. Mercury-gilding was invented by Chinese Daoism in the 4th century CE and was used for the gilding of bronze plaques. It was known to Pliny (33,20,64–5), Vitruvius (8,8,4) and in the early medieval period to Theophilus (De Diversis Artibus Book III).
In Europe, silver-gilt has always been more common than gilt-bronze, but in China the opposite has been the case. The ancient Chinese also developed the gilding of porcelain, which was later taken up by the French and other European potters.
Polished iron, steel and other metals are gilded mechanically by applying gold leaf to the metallic surface at a temperature just under red-hot, pressing the leaf on with a burnisher, then reheating when additional leaf may be laid on. The process is completed by cold burnishing.Alexander E. Youman, A Dictionary of Every-day Wants, p. 420, New York: Frank M. Reed, 1872.
"Overlaying" or folding or hammering on gold foil or gold leaf is the simplest and most ancient method, and is mentioned in Homer's OdysseyBook VI, 232: "And as when a man overlays silver with gold, a cunning workman whom Hephaestus and Pallas Athena have taught all manner of craft, and full of grace is the work he produces, even so the goddess shed grace upon his head and shoulders" from this translation and the Old Testament. The Ram in a Thicket (2600–2400 BC) from Ur describes this technique used on wood, with a thin layer of bitumen underneath to help adhesion.
The next advances involved two simple processes. The first involves gold leaf, which is gold that is hammered or cut into very thin sheets. Gold leaf is often thinner than standard paper today, and when held to the light is semi-transparent. In ancient times it was typically about ten times thicker than today, and perhaps half that in the Middle Ages.
If gilding on canvas or on wood, the surface was often first coated with gesso. "Gesso" is a substance made of finely ground gypsum or chalk mixed with glue. Once the coating of gesso had been applied, allowed to dry, and smoothed, it was re-wet with a sizing made of rabbit-skin glue and water ("water gilding", which allows the surface to be subsequently burnished to a mirror-like finish) or boiled linseed oil mixed with litharge ("oil gilding", which does not) and the gold leaf was layered on using a gilder's tip and left to dry before being burnished with a piece of polished agate. Those gilding on canvas and parchment also sometimes employed stiffly-beaten egg whites ("glair"), gum, and/or Armenian bole as sizing, though egg whites and gum both become brittle over time, causing the gold leaf to crack and detach, and so honey was sometimes added to make them more flexible.
Other gilding processes involved using the gold as pigment in paint: the artist ground the gold into a fine powder and mixed it with a binder such as gum arabic. The resulting gold paint, called shell gold, was applied in the same way as with any paint. Sometimes, after either gold-leafing or gold-painting, the artist would heat the piece enough to melt the gold slightly, ensuring an even coat. These techniques remained the only alternatives for materials like wood, leather, the vellum pages of illuminated manuscripts, and gilt-edged stock.
When the metal to be gilded is wrought or chased, the application of mercury before the amalgam is applied allows for it to be more easily spread. When the surface of the metal is plain, the amalgam can be applied to it directly. When no such preparation is applied, the surface to be gilded is simply bitten and cleaned with nitric acid. A deposit of mercury is obtained on a metallic surface by means of quicksilver water, a solution of mercury(II) nitrate, the nitric acid attacking the metal to which it is applied, and thus leaving a film of free metallic mercury.
After the amalgam is equally spread over the prepared surface of the metal, the mercury is then carefully volatilized with heat just sufficient to do so, as a temperature too high may cause part of the gold to be driven off, or otherwise run together, leaving some of the metal surface bare.
When the mercury has evaporated, indicated by the surface taking on a dull yellow color, the metal must undergo further steps to exhibit its fine gold color. First, the gilded surface is rubbed with a scratch brush of brass wire, until its surface is smooth. It is then covered with gilding wax, and again exposed to fire until the wax is burnt off. Gilding wax is composed of beeswax mixed with some of the following substances: red ochre, verdigris, copper scales, alum, vitriol, and borax. By this operation the color of the gilding is heightened, as a result of the perfect dissipation of some of the remaining mercury. The gilt surface is then covered over with potassium nitrate, alum or other salts, ground together, and mixed into a paste with water or weak ammonia. The piece of metal is then exposed to heat, before being quenching in water.
By this method, the color of the gilding is further improved and brought nearer to that of gold, probably by removing any particles of copper that may have been on the gilt surface. This process, when skillfully carried out, produces gilding of great solidity and beauty. This method of gilding metallic objects was formerly widespread, but fell into disuse as the dangers of mercury toxicity became known. Since fire-gilding requires that the mercury be volatilized to drive off the mercury and leave the gold behind on the surface, it is extremely dangerous. Breathing the fumes generated by this process can quickly result in serious health problems, such as neurology and endocrinology, since inhalation is a very efficient route for mercuric compounds to enter the body; the mercury used in the process also evaporates into the atmosphere, thus polluting it. This process has generally been supplanted by the electroplating of gold over a nickel substrate, which is more economical and less dangerous.
A number of different forms and compositions are available to apply gold to ceramic, and these include:Dodd, A.and Murfin, D. (1994) Dictionary Of Ceramics. The Institute Of Minerals.
The hairs on a gilder's tip are usually made of either blue squirrel hair or the hair of a badger (sometimes other hairs are also used, such as that of a camel) arranged in a single or double row along a flat ferrule made of wood or cardboard. In order to transfer the gold leaf, the hairs are first given a very light coating of adhesive by brushing them against a surface such as the back of the user's hand which has been coated with a thin layer of petroleum jelly (a common misconception is that static electricity causes the gold foil to attach to the brush, but this is not so) and then laying the edge of the brush along the edge of the piece of metal foil. The jelly will cause the metal to adhere very gently to the hairs and allow the piece to be floated from the paper surface on which had previously been stored. Because the leaf is so thin, this must be done in a room with extremely still air, and the user of the tip usually does not breathe until the leaf is in place.
Once the leaf has settled, it is often burnished with polished piece of agate to achieve a high degree of brilliance.
Gilder's tips are necessary because touching the metal leaf with the finger tips would immediately cause the leaf to lose its coherent flattened shape and crumble irretrievably into metallic dust which then cannot be used for any purpose.
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