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Saturday, 20 October 2012
Interior
Gilding
Gilding
The term gilding covers
a number of decorative techniques for applying fine gold
leaf or
powder to solid surfaces such as wood, stone, or metal to give a thin coating
of gold. A gilded object is described as "gilt". Where metal is
gilded it was traditionally usually silver in
the West, to make silver-gilt (or "vermeil") objects, but gilt-bronze
is much used in China, and also called ormolu if it is Western.
Methods of gilding include hand application and gluing, chemical gilding, and electroplating,
the last also called gold plating.[1]Parcel-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 un-gilt areas.
Origins and spread
of gilding
Herodotus mentions that the Egyptians gilded wood and metals, and
many such objects have been excavated. Certain Ancient Greek statues of great
prestige werechryselephantine, i.e. made of gold-plated wood (for the clothing) and ivory (for the flesh); most famously those of Zeus in Olympia and Athena Parthenos in the Parthenon. Extensive ornamental
gilding was also used in the ceiling coffers of the Propylaea. Pliny the Elder informs us that the first gilding seen at Rome was after the destruction ofCarthage, under the censorship of
Lucius Mummius, when the Romans began to gild the ceilings of their temples and
palaces, the Capitol being the first place on
which this process was used. But he adds that luxury advanced on them so
rapidly that in very little time you might see all, even private and poor
people, gild the walls, vaults, and other parts of their dwellings. Owing to
the comparative thickness of the gold leaf used in ancient gilding, the traces
of it which yet remain are remarkably brilliant and solid. Fire-gilding of
metal goes back at least to the 4th century BC, and was known to Pliny
(33,20,64–5) and Vitruvius (8,8,4).
Gilding
processes
Modern gilding is applied to
numerous and diverse surfaces and by various processes; those used in modern
technology are described in gold plating. More traditional techniques still
form an important part of frame making and are sometimes still
employed in general woodworking, cabinet-work, decorative painting
and interior decoration, bookbinding, and ornamental leatherwork, and in the decoration
of pottery, porcelain, and glass.
Mechanical
Gilding
Mechanical gilding includes
all the operations in which gold leaf is prepared, and the processes to
mechanically attach the gold onto surfaces. The techniques include burnishing,
water gilding and oil-gilding used by wood carvers and gilders; and the gilding
operations of the house decorator, sign painter, bookbinder, the appertained
and several others.
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 burnished, then
reheating when additional leaf may be laid on. The process is completed by cold
burnishing.
"Overlaying" or
folding or hammering on gold foil or gold leaf is the simplest and most ancient
method, and is mentioned in Homer's Odyssey (Bk vi, 232),[2] and
the Old Testament.
The Ram in a Thicket of about 2600-2400
BC from Ur uses this technique 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 10 times thicker than today, and perhaps half that in the Middle Ages. The object being
gilded was coated with adhesive, usually 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 is re-wet with glue waster or size and the gold leaf was layered
on and left to dry. A second gilding process was using the gold as pigment in
paint. The artist ground the gold into a fine powder and mixed it with a
binder. Then the gold was applied 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
alternative for materials like wood, leather, and the vellum pages of illuminated manuscripts.
Cold gilding
In this process the gold
is obtained in a state of extremely fine division, and applied by mechanical
means. Cold gilding on silver is performed by a solution of gold in aqua regia, applied by dipping a linen rag into the solution,
burning it, and rubbing the black and heavy ashes on the silver with the finger
or a piece of leather or cork.
Wet gilding
Wet gilding is effected by means of a dilute solution of gold(III) chloride with twice its quantity of ether. The liquids are agitated and allowed to rest, when the
ether separates and floats on the surface of the acid. The whole mixture is
then poured into a funnel with a small aperture, and allowed to rest for some
time, when the acid is run off and the ether separated. The ether will be found
to have taken up all the gold from the acid, and may be used for gilding iron
or steel, for which purpose the metal is polished with fine emery and spirits
of wine. The ether is then applied with a small brush, and as it evaporates it
deposits the gold, which can now be heated and polished. For small delicate
figures, a pen or a fine brush may be used for laying on the ether solution.
The gold(III) chloride can also be dissolved in water in electro less plating
wherein the gold is slowly reduced out of solution onto the surface to be
gilded. When this technique is used on the second surface of glass and backed
with silver, it is known as "Angel gilding
Fire-gilding
Fire-gilding or Wash-gilding is a process by which an amalgam of gold is applied to
metallic surfaces, the mercury being subsequently volatilized, leaving a film of gold or
an amalgam containing from 13 to 16% of mercury. In the preparation of the
amalgam the gold must first be reduced to thin plates or grains, which are
heated red hot, and thrown into previously heated mercury, until it begins to
smoke. Upon stirring the mercury with an iron rod, the gold totally disappears.
The proportion of mercury to gold is generally six or eight to one. When the
amalgam is cold it is squeezed through chamois leather to separate the superfluous mercury; the gold, with about
twice its weight of mercury, remains behind, forming a yellowish silvery mass
with the consistency of butter.
Depletion gilding
In depletion gilding, a
subtractive process discovered in Pre-Columbian Mesoamerica, articles are fabricated by various techniques from an
alloy of copper and gold, named tumbaga by the Spaniards. The surface is etched with acids, resulting in a
surface of porous gold. The porous surface is then burnished down, resulting in
a shiny gold surface. The results fooled the conquistadors into thinking they
had massive quantities of pure gold. The results startled modern archaeologists, because at first the pieces resemble electroplated
articles. Keum-boo is a special Korean technique of silver-gilding, using depletion gilding.
Ceramics
The gilding of
decorative ceramics has been undertaken for centuries, with the permanence
and brightness of gold appealing to designers. Both porcelain and earthenware are commonly decorated with gold, and in the late 1970s
it was reported that 5 tonnes of gold were used annually for the decoration of
these products.[3] Some wall tiles also have gold decoration. Application techniques include spraying, brushing, banding
machines and direct or indirect screen-printing. After application the decorated ware is
fired in kiln to fuse the gold to the glaze and hence ensure its parlance. The most important factors
affecting coating quality are the composition of applied gold, the state of the
surface before application, the thickness of the layer and the firing
conditions.
See also
- Gilding metal - imitation gold
- Metal leaf
- Gilded Age
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