(i) Types and application
Written sources from as early as the late 3rd century AD describe the tinting of metals in imitation of gold, as well as the alloying of gold and silver with base metals. Gold may be naturally or deliberately colored by the presence of traces of metals such as copper, iron or silver. These also alter its hardness. Gold leaf is obtained today in various shades and degrees of hardness, pure 24 carat gold being the softest. Tinted silver was widely used on polychrome sculpture, in interior decoration and on furniture, notably in 17th- and 18th-century Europe. Tin leaf, which does not tarnish, was colored to imitate gold in addition to being used alone. Leaf is also now produced from white gold, palladium and platinum; aluminum may be used as a cheap alternative.
A laminated leaf, resembling gold leaf, was made by placing a thin sheet of gold over a similar sheet of silver (or tin) and hammering the two together. The gold–silver laminate is known as Zwischgold (Ger.), partijtgoud (Dut.) or or parti (Fr.); according to Skaug (1993), the Italian oro di metà refers to the same material. Unlike pure gold leaf, however, it tarnishes, as the thin gold cannot protect the silver below. The gold–tin leaf was rather more robust than gold leaf and has been identified in 14th- and 15th-century Italian mural paintings. Gold-colored alloys used for leaf include the copper–zinc Schlagmetall (‘beaten metal’) or ‘Dutch metal’, used from the 19th century. The use of copper–tin alloy leaf (now blackened) has been reported in the frescoes (c. 1305) attributed to Giotto and his school in the Arena Chapel, Padua; this may correspond to the little-known orpello (‘tinsel’), occasionally referred to in 14th- and 15th-century Italian documents.
The manual method of hammering gold into leaf is known as goldbeating, and medieval European guild statutes indicate that it was a separate, although related, trade to that of goldsmiths and other workers in precious metals. Although the process was successfully automated in the 1920’s, the basic procedure has remained essentially unchanged over the centuries. A small gold ingot is pressed between steel rollers to give a continuous ribbon 25μm thick and about 50 mm wide; 200 squares (50×50 mm) cut from it are interleaved with sheets of parchment 100 mm square; this pack or ‘cutch’, bound in parchment, is beaten until the gold extends to the edges of the parchment. The pieces are quartered and the process repeated. The gold is quartered again; 800 pieces are placed in a ‘shoder’ of goldbeater’s skins (prepared from ox gut) and beaten, this procedure being carried out twice. Lastly, the leaf is beaten in a ‘mould’ of very thin skins, cleaned with calcined gypsum powder. It is cut, on a leather cushion, into pieces 80 mm square and inserted loose between sheets of rouged tissue into a book containing 25 leaves. According to Cennino Cennini, late 14th-century Italian goldbeaters could obtain 145 leaves, similar in size to modern leaf, from a Venetian ducat, which, at that time, weighed about 3.5 g. The thickness of such leaf can be estimated to have been about 0.2μm (0.0002 mm). Modern leaf can be even thinner—c. 0.1μm if machine made, c. 0.05μm if hand beaten. At this thickness, it is translucent, transmitting greenish light. Transfer gold leaf (patent gold) is loosely attached to sheets of tissue by pressing and can be used only for oil gilding. It was first made in strip form in the early 20th century, providing a more convenient format for gilding vehicles; in the 1930’s a method of sputtering gold on to the waxed paper carrier was devised. Modern foil is manufactured by vaporizing the gold; the carrier film is polyester. It can be obtained with a brilliant metallic finish and is used extensively in manufacturing industries for gold decoration.
An artifact can be gilded using simple, unpigmented adhesives; the choice depends partly on the effect desired and the nature of the substrate. Resin-like substances and oil/resin varnish mixtures have been used for gilding textiles. In Japan, for example, gold or silver leaf was applied to cloth during the Momoyama period (1568–1600) using a technique copied from imported Chinese textiles. Such plant gums as gum Arabic have been widely employed for gilding materials as diverse as ivory, wood, parchment and paper. Other simple adhesives have included beaten egg white (glair), used in manuscript illumination and for gilding leather, and shellac, also used for the latter. The use of such other substances as garlic juice is recorded in historical sources.
Water gilding and oil or mordant gilding are the two main methods of applying gold leaf used, notably on easel and wall paintings, furniture and sculpture, since medieval times. Water gilding was certainly known in Europe by the early 12th century. This method is used where a shining burnished finish, imitating solid metal, is desired, for example in the gold backgrounds of icons and medieval altarpieces and in manuscript illumination. Gold applied using an oil mordant cannot be burnished, as the adhesive holds the gold too firmly; it therefore appears yellower and has a diffusely reflecting surface. This difference in appearance may be exploited by using both types of gilding in the same piece of work.
In water gilding the object is usually coated with several layers of gesso or chalk mixed with parchment size. When this is hard, it is scraped and polished to a perfectly smooth finish. A soft, slightly greasy, reddish-colored clay, known as bole, mixed with dilute size, is then applied and, when dry, burnished or polished. A sheet of leaf is placed on a padded leather gilder’s cushion, cut to size if necessary and picked up using a gilder’s tip—a thin, flat, hair brush (in medieval times, tweezers and card would have been used). The bole is moistened with water to which a little size may be added. The leaf is held above it, just touching the surface, and is sucked on to the bole by capillary action. It may be patted down afterwards if necessary. When the work is dry, the gold is burnished; modern burnishing tools are usually made of agate, but in earlier times, hematite and even dogs’ teeth were used.
For oil, gilding a mordant, consisting principally of linseed oil heated with a lead drier, is used; frequently a natural resin varnish is also incorporated. The mordant may be pigmented (e.g. with yellow ochre), which not only enables the design seen on the surface to be decorated but may also help to disguise small flaws in the gilding. The mordant is painted on and left until tacky, when the gold is applied; this technique is used for delicate linear designs or lettering.
Gold and silver leaf were applied to, or encased in, glass to produce the gold and silver tesserae that profoundly influenced the character of post-Antique and medieval mosaics. According to medieval sources, such as the Compositiones variae (Lucca, Bib. Capitolare, MS. 490), the leaf was placed on a small thick sheet of glass, and covered with a very thin glass sheet and heated in a furnace until the glass began to melt; later sources suggest the use of powdered glass, giving a very thin surface layer. After cooling, the surface of the thinner glass was polished with emery powder or a similar abrasive. The slab was then broken into square tesserae. Variations in the appearance of the gold could be obtained by the deliberate use of brownish or greenish glass, rather than colorless, and by applying the tesserae upside down, with the thicker glass at the top.
C. Cennini: Il libro dell’arte (MS.; c. 1390); ed. F. Brunello (Vicenza, 1971); Eng. trans. and ed. by D. V. Thompson, as The Craftsman’s Handbook: The Italian ‘Il libro dell’arte’ (New Haven, 1933, R/New York, 1960), pp. 60–63, 79–89, 96–8, 100–04, 106–8, 112–13, 118–19
W. Lewis: Commercium philosophico-technicum, 2 vols. (London, 1763–5), i, pp. 38–229
C. Singer, ed.: A History of Technology, 7 vols. (Oxford, 1954–78), i, pp. 581–2, 623–62, 677; ii, pp. 174, 342–3
S. M. Alexander: ‘Medieval Recipes Describing the Use of Metals in Manuscripts’, Marsyas, xii (1964–5), pp. 34–51
C. S. Smith and J. G. Hawthorne: ‘Mappae Clavicula: A Little Key to the World of Medieval Techniques’, Trans. Amer. Philos. Soc., n.s., lxiv (1974), pp. 3–122 [especially p. 48]
B. J. Sitch: ‘Transferable Gold Coatings: Historical and Technical Aspects of their Development’, Gold Bull., xi (1978), pp. 110–15
E. D. Nicholson: ‘The Ancient Craft of Gold Beating’, Gold Bull., xii (1979), pp. 161–6
P. MacTaggart and A. MacTaggart: Practical Gilding (Welwyn, 1984)
M. Matteini and A. Moles: ‘Le tecniche di doratura nella pittura murale’, Le pitture murali: Tecniche, problemi, conservazione, eds C. Danti, M. Matteini and A. Moles (Florence, 1990), pp. 121–6, 148–9
A. Meyer: ‘Mosaik’, Reclams Handbuch der künstlerischen Techniken, ii (Stuttgart, 1990), pp. 399–498 [especially pp. 427–9]
D. Bigelow, E. Cornu, G. J. Landrey and C. van Horne, eds: Gilded Wood: Conservation and History (Madison, 1991)
Gilding and Surface Decoration: Preprints of the UKIC Conference Restoration ’91: London, 1991
E. Skaug: ‘Cenniniana: Notes on Cennino Cennini and his Treatise’, A. Crist., lxxxi/754 (1993), pp. 15–22
L. L. Brownrigg, ed.: Making the Medieval Book: Techniques of Production (Los Altos Hills, CA, 1995)
E. Becker: Gold Leaf Application and Antique Restoration (Atglen, 1998)
A. Bartl and M. Lautenschlager: ‘Wie man sol machen ein güte goltz grunndt: Anweisungen zur Blanzvergoldung in der Buchmaleri’, Restauro, cvi/3 (2000), pp. 180–87
T. Drayman-Weisser: Gilded Metals: History, Technology and Conservation (London, 2000)
K. P. Whitley: The Gilded Page: The History and Technique of Manuscript Gilding (New Castle, DE, 2000)
A burnished water gilded surface may be decorated by the use of ornamental punches and incised lines while the gesso is fresh enough to be sufficiently flexible. The punch is held at right angles to the gilded surface and tapped lightly with a hammer, thus indenting the gesso ground without breaking the surface. Combinations of punches, the designs of which may range from simple circles or rings to complex rosettes and leaf shapes, are used to create patterns. A stylus may also be used to indent lines, often combined with patterns produced by a punch. Rich and complex textural effects may thus be achieved. This technique probably evolved from the use of iron punches and gravers to produce raised decoration in sheet metal and from blind tooling (decorative punching without the use of gold), which developed in Europe for the decoration of leather, particularly for book bindings, certainly by the 11th century AD. Gold-tooling of leather, although a very old technique in the Middle East, reached Europe only in the 15th century; ‘gilt’ leather, however, had been produced in the late 14th century. In China, metal leaf was used in conjunction with the lacquer to decorate Tang mirrors in such Southern Song (1127–1297) techniques as qiangjin, in which gold leaf was tooled into depressions incised into the surface of the lacquer.
Metal leaf can also be painted, either with opaque paint or with translucent glazes; opaque and transparent paints can also be used together. Opaque paint may be used to paint a design over gold, but its most effective use is in the sgraffito technique: areas of color are painted over the gold and then scraped off when the paint is partly dry, revealing the gold beneath in the desired pattern. Richly detailed effects may be obtained, particularly in the representation of brocades and other textiles, for example in 14th- and 15th-century European altarpieces where egg tempera paint has been applied to burnished gold. Transparent glazes are applied thinly, in an oil-based medium, to reduce the brilliance of the metal as little as possible. They were widely used on painted altarpieces and in 17th- and 18th-century Europe on polychrome sculpture, leather items and other decorative objects. Gamboge, saffron and the evaporated juice from certain species of aloe were among the yellow colorants; red colorants included lac dye and dragon’s blood. Annatto gave an orange, and green could be obtained using verdigris. A number of synthetic organic dyestuffs are available; certain pigments, such as alizarin crimson or Prussian blue, are also suitable.
E. Skaug: ‘Punch Marks—What Are they Worth? Problems of Tuscan Workshop Interrelationships in the Mid-fourteenth Century: The Ovile Master and Giovanni da Milano’, La pittura nel XIV e XV secolo: Il contributo dell’analisi tecnica alla storia dell’arte: Atti del XXIV congresso internazionale di storia dell’arte: Bologna, 1979 (Bologna, 1983), pp. 253–82
R. E. Straub: ‘Tafel- und Tüchleinmalerei des Mittelalters’, Reclams Handbuch der künstlerischen Techniken, i (Stuttgart, 1984), pp. 189–98, 229–36
Art in the Making: Italian Painting before 1400 (exh. cat. by D. Bomford and others; London, N.G., 1989–90), pp. 24–6, 130–35
C. Cession: ‘The Surface Layers of Baroque Gildings: Examination, Conservation, Restoration’, Cleaning, Retouching and Coatings: Preprints of the Contributions to the IIC Brussels Congress, 1990, pp. 33–5
E. S. Skaug: Punch Marks from Giotto to Fra Angelico: Attribution, Chronology, and Workshop Relationships in Tuscan Panel Painting: With Particular Consideration to Florence, c. 1330–1430 (Oslo, 1994)
J. LaFerla: Gilding: Easy Techniques & Elegant Projects with Metal Leaf (New York, 1997)
M. S. Frinta: Punched Decoration on Late Medieval Panel and Miniature Painting (Prague, 1998)
K. Skinner: The Gilded Room: Decorating with Metallic Effects, from Metal Leaf to Powder, Pastes & Paints (New York, 2000)
A.-M. Hacke, C.M. Carr and A. Brown: ‘Characterisation of Metal Threads in Renaissance Tapestries’, Scientific Analysis of Ancient and Historic Textiles, ed. P. Wyeth (London, 2005), pp. 71–9
M. Járó: ‘The Gold Threads in the Hungarian Coronation Mantle’, The Coronation Mantle of the Hungarian Kings, ed. I. Bardoly (Budapest, 2005)