Gold leaf is gold that has been hammered into thin sheets (usually around 0.1 μm thick) by a process known as goldbeating, for use in gilding. Gold leaf is a type of metal leaf, but the term is rarely used when referring to gold leaf. The term metal leaf is normally used for thin sheets of metal of any color that do not contain any real gold. Gold leaf is available in a wide variety of karats and shades. The most commonly used gold is 23-karat gold. Traditional water gilding is the most difficult and highly regarded form of gold leafing. It has remained virtually unchanged for hundreds of years and is still done by hand.
History
Five thousand years ago, Egyptian artisans recognized the extraordinary durability and malleability of gold and became the first goldbeaters and gilders. They pounded gold using a round stone to create the thinnest leaf possible. Apart from the introduction of the cast-iron hammer and a few other innovations, the tools and techniques remained virtually unchanged for thousands of years until the modern invention of roller presses. Gold-leaf forging is first known from Turkey about 8000 years ago. It is a traditional handicraft in Nanjing (China), produced as early as the Three Kingdoms (220–280 AD) and Two Jins (266–420) dynasties; it was used in Buddha-statue manufacturing and construction. It was widely used in the gilding of Buddha statues and idols and in the construction industry during the Eastern Wu (222–280) and Eastern Jin (266–420) dynasties. During the Qing dynasty (1640–1912), the technology developed, and Nanjing gold leaf was sold overseas. It retains traditional smelting, hand-beating and other techniques, and the gold leaf is pure, uniform and soft. On May 20, 2006, it was included in the first batch of national intangible cultural heritage representative items. Modern gold-leaf artists combine ancient traditional crafts with modern technology to make traditional gold leaf. Forging skills are more sophisticated. Gold-foil production in Nanjing follows the ancient production process. The forging process has been tempered by more than a dozen processes such as gold bar, leaf beat, twisting, opening, assembly, issuing, and foil cutting. It is also called "playing gold leaf". According to the needs of different products, a proportion of silver and copper is added; the metal is then melted into liquid form, poured into an iron tank, cooled to form gold bars, hammered into thin slices, cut into small gold pieces, and then covered with gold foil and hammered into gold foil repeatedly at high temperature.
Production
The process of hammering gold into leaf is known as goldbeating. The karat and color of gold leaf vary depending on the amount of silver or copper added to the gold. Most goldbeaters make 23 karat leaf. The gold and its alloy are put in a crucible and melted in a furnace. The liquid gold is poured into a mold to cast it into a bar. The bar of gold is put through a rolling mill repeatedly. Each time through the mill, the rollers are adjusted closer and closer to each other, to make the gold thinner and thinner. The bar is rolled to a thickness of 25 micrometres (1⁄1000 in). After rolling, the ribbon of gold is cut into 2.5-centimetre (1 in) squares. The first step in the beating process is called the cutch. The cutch is made up of approximately 150 skins. In the early days of the trade, ox intestine membrane (goldbeater's skin) was used to interleave the gold as it was beaten. Today other materials, such as Mylar, are used. Using wooden pincers, the preparer picks up each square of gold and places it in the center of each skin. When the cutch is filled with the small gold squares, it is wrapped in several bands of parchment which serve to hold the packet together during the beating. Parchment is still the best material known to withstand the hours of repeated hammer blows needed to beat the gold.
The gold is beaten on a large, heavy block of marble or granite. These stone blocks were sometimes placed on top of a tree trunk set deep into the ground. This created greater resilience for the hammer. Beating of the cutch by hand takes about one hour using a 7-kilogram (15 lb) hammer. The goldbeater follows a pattern and sets up a rhythm, striking the packet with up to seventy strokes a minute. The packet is rotated and turned over to ensure that the gold inside expands evenly in all directions. The original small squares of gold are beaten until they have expanded to the outer edges of the 10 cm (4 in) square cutch. The gold is taken out of the cutch and each piece is cut into four pieces with a knife. Using the pincers, these squares of gold are put into a second packet called the shoder, which has approximately 1,500 skins. The shoder is beaten for about three hours until the gold has expanded to a 13 cm (5 in) square. The gold is taken out of the shoder and placed on a leather-covered surface. The gold is thin enough now that the cutter can simply blow on it to flatten it out. Using a wooden implement called a wagon, the gold is quickly cut into four pieces and immediately placed in a packet called a mold for the final beating. The wagon has sharp cutting blades, traditionally made from malacca cane (rattan). The mold contains 1,500 pieces of gold. Before the mold is filled with gold, the skins are coated with a gypsum powder. This process prevents the delicate gold leaf from sticking to the skins. The mold is beaten with an 3.6-kilogram (8 lb) hammer for three to four hours until it has been beaten into a circle about 15 centimetres (6 in) in diameter. The finished leaf forms an unbroken sheet of gold with a thickness of approximately 100 nanometres (1⁄250000 in). After the leaves are taken out of the mold, they are conventionally cut into a 8.6-centimetre (3.375 in) square and packaged in tissue-paper books containing twenty-five leaves.
Uses
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