Gilding and Iconography

Gilding Arts Studio

This page is currently still under construction. I expect to have it reasonably functional by the end of this monsoon !

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Casein Paint

Casting

Lost-Wax Casting

Cennino d'Andrea Cennini

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Denatured Alcohol

Ductility

Dutch Metal

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Embossing

Enamel Paint

Ethanol

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Foil

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Gesso

Gilding

Mechanical Water Gilding, Oil Gilding

Chemical Cold Gilding, Wet Gilding, Fire Gilding

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Investment casting

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Karat

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Lost Wax Casting

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Acetone

Acetone is a good solvent for most plastics and synthetic fibers including those used in laboratory bottles made of polystyrene, polycarbonate and some types of polypropylene.It is ideal for thinning fiberglass resin, cleaning fiberglass tools and dissolving two-part epoxies and superglue before hardening. It is used as a volatile component of some paints and varnishes. As a heavy-duty degreaser, it is useful in the preparation of metal prior to painting; it also thins polyester resins, vinyl and adhesives.

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Acrylic Paint

Acrylic paint is fast drying paint containing pigment suspension in acrylic polymer emulsion. Acrylic paints can be diluted with water, but become water-resistant when dry. Depending on how much the paint is diluted (with water) or modified with acrylic gels, media, or pastes, the finished acrylic painting can resemble a watercolor or an oil painting, or have its own unique characteristics not attainable with other media.

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Alloy

An alloy is a metallic solid solution composed of two or more elements. Alloying a metal is done by combining it with one or more other metals or non-metals that often enhances its properties.

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Annealing

Annealing in metallurgy is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and then cooling. Annealing is used for inducing ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by substantially heating the material (generally until glowing) for a while and allowing it to cool. Unlike ferrous metals—which must be cooled slowly to anneal—copper, silver and brass can be cooled slowly in air or quickly by quenching in water. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming.

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Aqua Regia

Aqua regia (Latin: royal water) or aqua regis is a highly corrosive, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing nearly pure nitric acid and maximum-concentration (38%) hydrochloric acid, usually in a volume ratio of 1:3 respectively. It was named so because it can dissolve the so-called royal metals, or noble metals, gold and platinum. However, ruthenium, tantalum, iridium, osmium, titanium, rhodium and a few other metals are capable of withstanding chemical attack from it.

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Armenian Bole

Armenian Bole, also known as bolus armenus or bole armoniac, is an earthy clay, usually red, native to Armenia. It is red due to the presence of iron oxide; the clay also contains hydrous silicates of aluminum and possibly magnesium. It is applied during gilding as a base for the gold leaf and to give greater depth and luster.

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Beeswax

Beeswax is a natural wax produced in the bee hive of honey bees of the genus Apis. It is mainly esters of fatty acids and various long chain alcohols. Typically, for a honey bee keeper, 10 pounds of honey yields 1 pound of wax.

Beeswax was ancient man's first plastic, and for thousands of years has been used as a modeling material, to create sculpture and jewelry molds for use in the lost-wax casting process, or cire perdue. Lost-wax casting of metals involved coating of a wax model with plaster, melting the wax out of the resulting mould and filling the space with molten metal. The technique is still used today by jewellers, goldsmiths and sculptors, in dentistry and even in the industrial manufacture of complex components by investment casting of metals.

It is also used for creating various finishes in combination with paints, steel wool and shellac etc., or as a component of furniture polish, dissolved in turpentine, sometimes blended with linseed or tung oil.

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Bitumen

Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum that is so thick and heavy that it must be heated or diluted before it will flow. At room temperature, it has a consistency much like cold molasses.Refined bitumen is the residual (bottom) fraction obtained by fractional distillation of crude oil. It is the heaviest fraction and the one with the highest boiling point, boiling at 525 °C (977 °F).

Bitumen was the nemesis of many artists during the 19th century. Although widely used for a time, it ultimately proved unstable for use in oil painting, especially when mixed with the most common dilutents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with other colors to render a darker tone resulted in the eventual deterioration of a good many paintings, those of Delacroix being just one notable example.

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Brass

Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.

In comparison, bronze is principally an alloy of copper and tin. Bronze does not necessarily contain tin, and a variety of alloys of copper, including alloys with arsenic, phosphorus, aluminum, manganese, and silicon, are commonly termed "bronze". The term is applied to a variety of brasses and the distinction is largely historical.

Brass has a muted yellow colour, which is somewhat similar to gold. It is relatively resistant to tarnishing, and is often used as decoration and for coins. In antiquity, polished brass was often used as a mirror.

Admiralty brass contains 30% zinc, and 1% tin which inhibits dezincification in many environments.
Aich's alloy typically contains 60.66% copper, 36.58% zinc, 1.02% tin, and 1.74% iron. Designed for use in marine service owing to its corrosion resistance, hardness and toughness. A characteristic application is to the protection of ships' bottoms, but more modern methods of cathodic protection have rendered its use less common. Its appearance resembles that of gold.
Alpha brasses with less than 35% zinc, are malleable, can be worked cold, and are used in pressing, forging, or similar applications. They contain only one phase, with face-centered cubic crystal structure. Prince's metal or Prince Rupert's metal is a type of alpha brass containing 75% copper and 25% zinc. Due to its beautiful yellow color, it is used as an imitation of gold. The alloy was named after Prince Rupert of the Rhine.
Alpha-beta brass (Muntz metal), also called duplex brass, is 35–45% zinc and is suited for hot working. It contains both α and β' phase; the β'-phase is body-centered cubic and is harder and stronger than α. Alpha-beta brasses are usually worked hot.
Aluminium brass contains aluminium, which improves its corrosion resistance. It is used for seawater service and also in Euro coins (Nordic gold).
Arsenical brass contains an addition of arsenic and frequently aluminium and is used for boiler fireboxes.
Beta brasses, with 45–50% zinc content, can only be worked hot, and are harder, stronger, and suitable for casting.
Cartridge brass is a 30% zinc brass with good cold working properties. Used for ammunition cases.
Common brass, or rivet brass, is a 37% zinc brass, cheap and standard for cold working.
DZR brass is dezincification resistant brass with a small percentage of arsenic.
Gilding metal is the softest type of brass commonly available. An alloy of 95% copper and 5% zinc, gilding metal is typically used for ammunition "jackets", e.g. full metal jacket bullets.
High brass contains 65% copper and 35% zinc, has a high tensile strength and is used for springs, screws, and rivets.
Leaded brass is an alpha-beta brass with an addition of lead. It has excellent machinability.
Lead-free brass as defined by California Assembly Bill AB 1953 contains "not more than 0.25 percent lead content".
Low brass is a copper-zinc alloy containing 20% zinc with a light golden colour and excellent ductility; it is used for flexible metal hoses and metal bellows.
Manganese brass is a brass most notably used in making golden dollar coins in the United States. It contains roughly 70% copper, 29% zinc, and 1.3% manganese.
Muntz metal is about 60% copper, 40% zinc and a trace of iron, used as a lining on boats.
Nickel brass is composed of 70% copper, 24.5% zinc and 5.5% nickel used to make pound coins in the pound sterling currency.
Naval brass, similar to admiralty brass, is 40% zinc and 1% tin.
Nordic gold, used in 10, 20 and 50 cts euro coins, contains 89% copper, 5% aluminium, 5% zinc, and 1% tin.
Red brass is both an American term for the copper-zinc-tin alloy known as gunmetal, and an alloy which is considered both a brass and a bronze. It typically contains 85% copper, 5% tin, 5% lead, and 5% zinc. Red brass is also an alternative name for copper alloy C23000, which is composed of 14–16% zinc, 0.05% iron and lead, and the remainder copper. It may also refer to ounce metal, another copper-zinc-tin alloy.
Rich low brass (Tombac) is 15% zinc. It is often used in jewelry applications.
Tonval brass (also called CW617N or CZ122 or OT58) is a copper-lead-zinc alloy. It is not recommended for seawater use, being susceptible to dezincification.
White brass contains more than 50% zinc and is too brittle for general use. The term may also refer to certain types of nickel silver alloys as well as Cu-Zn-Sn alloys with high proportions (typically 40%+) of tin and/or zinc, as well as predominantly zinc casting alloys with copper additive.
Yellow brass is an American term for 33% zinc brass.

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Bronze Sculpture

Bronze is the most popular metal for cast metal sculptures; a cast bronze sculpture is often called simply a "bronze".

Common bronze alloys have the unusual and desirable property of expanding slightly just before they set, thus filling the finest details of a mold. Their strength and ductility (lack of brittleness) is an advantage when figures in action are to be created, especially when compared to various ceramic or stone materials (such as with marble sculpture). These qualities allow the creation of extended figures, as in Jeté, or figures that have small cross sections in their support, such as the equestrian statue of Richard the Lionheart. Modern statuary bronze is 90% copper and 10% tin; older bronze alloys varied only slightly from this composition.

But the value of the bronze for other uses is disadvantageous to the preservation of sculptures; few large ancient bronzes have survived, as many were melted down to make weapons in times of war or to create new sculptures commemorating the victors, while far more stone and ceramic works have come through the centuries, even if only in fragments.

The great civilizations of the old world worked in bronze for art, from the time of the introduction of the alloy for edged weapons. The Greeks were the first to scale the figures up to life size. Few examples exist in good condition; one is the seawater-preserved bronze now called "The Victorious Athlete," which required painstaking efforts to bring it to its present state for museum display. Far more Roman bronze statues have survived. The ancient Chinese, from at least 1200BC, knew both lost-wax casting and section mould casting, and in the Shang dynasty created large ritual vessels covered with complex decoration which have survived in tombs. Over the long creative period of Egyptian dynastic art, small lost-wax bronze figurines were made in large numbers; several thousand of them have been conserved in museum collections. From these beginnings, bronze art has continued to flourish.

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Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal. However, since "bronze" is a somewhat imprecise term, and historical pieces have variable compositions, in particular with an unclear boundary with brass, modern museum and scholarly descriptions of older objects increasingly use the more cautious and inclusive term "copper alloy" instead.

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Burnishing

Burnishing is the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a rough surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield strength of the material.

Metal Leaf can be burnished when there is a substrate of gesso as in water gilding.

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Casein paint

Casein paint derived from milk casein, is a fast-drying, water-soluble medium used by artists. It generally has a glue-like consistency, but can be thinned with water to the degree that fits a particular artist's style and desired result. It can be used on canvas panels, illustration boards, paper, wood and masonite. Because the dried paint film is inflexible and brittle, it is not appropriate to be applied in heavy impastos on flexible supports such as canvas. Casein paint is reworkable and can be used for underpainting. It generally dries to a matte finish.

Casein paint has been used since ancient Egyptian times as a form of tempera paint, and is still used today. Some of the qualities that artists value casein paint for is that unlike gouache, it dries to an even consistency making it ideal for murals. Also, visually it can resemble oil painting more than most other water based paints, and works well as an underpainting.

A quick way to make casein painting medium is to take some skim milk cottage cheese and first wash off any of the milky fluids. The lumps of casein left behind are then dissolved by adding, in a pot, water and some ammonia. The ammonia should be preferably in the form of ammonium carbonate. As the mixture is stirred while it warms it begins to froth and the lumps dissolve. It is not boiled but kept simmering and stirred until the frothing stops. After the syrup is cooled, that is the medium. It keeps in a refrigerator for about four days.

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Casting

In metalworking, casting involves pouring a liquid metal into a mold, which contains a hollow cavity of the desired shape, and then is allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Metal casting processes uses the following terminology:

Pattern: An approximate duplicate of the final casting used to form the mold cavity.
Molding material: The material that is packed around the pattern and then the pattern is removed to leave the cavity where the casting material will be poured.
Flask: The rigid wood or metal frame that holds the molding material.
- Cope: The top half of the pattern, flask, mold, or core.
- Drag: The bottom half of the pattern, flask, mold, or core.
Core: An insert in the mold that produces internal features in the casting, such as holes.
- Core print: The region added to the pattern, core, or mold used to locate and support the core.
Mold cavity: The combined open area of the molding material and core, there the metal is poured to produce the casting.
Riser: An extra void in the mold that fills with molten material to compensate for shrinkage during solidification.
Gating system: The network of connected channels that deliver the molten material to the mold cavities.
- Pouring cup or pouring basin: The part of the gating system that receives the molten material from the pouring vessel.
- Sprue: The pouring cup attaches to the sprue, which is the vertical part of the gating system. The other end of the sprue attaches to the runners.
- Runners: The horizontal portion of the gating system that connects the sprues to the gates.
- Gates: The controlled entrances from the runners into the mold cavities.
Vents: Additional channels that provide an escape for gases generated during the pour.
Parting line or parting surface: The interface between the cope and drag halves of the mold, flask, or pattern.
Draft: The taper on the casting or pattern that allow it to be withdrawn from the mold
Core box: The mold or die used to produce the cores.

see Lost-Wax Casting

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Cennino d'Andrea Cennini

Cennino d'Andrea Cennini (c. 1370 – c. 1440) was an Italian painter influenced by Giotto. He was a student of Agnolo Gaddi. Gaddi trained under his father, called Taddeo Gaddi, who trained with Giotto.

Cennini was born in Colle Val d'Elsa, Tuscany.

He is remembered mainly for having authored Il libro dell'arte, often translated as The Craftsman's Handbook. At first thought to be written in the early 15th century, the book is a "how to" on Renaissance art. It contains information on pigments, brushes, panel painting, the art of fresco, and techniques and tricks, including detailed instructions for underdrawing, underpainting and overpainting in egg tempera. Cennini also provides an early, if somewhat crude, discussion of painting in oils. His discussion of oil painting was important for dispelling the myth, propagated by Giorgio Vasari and Karel Van Mander, that oil painting was invented by Jan van Eyck (although Theophilus (Roger of Helmerhausen) clearly gives instructions for oil-based painting in his treatise, On Divers Arts, written in 1125).

The dates of Cennini's life are highly speculative. It is often falsely assumed that he was alive in 1437 because that date appears on one of the copies of his manuscript. This is discussed by Daniel V. Thompson in the preface to his authoritative translation of Il libro dell'arte. Thompson himself does not speculate on Cennini's years of life, a sure indication of the lack of evidence on this point. Thus, dating Cennini's book to the "early 15th century" as above is only a guess. The techniques Cennini describes are grounded in the late 13th and mid 14th centuries. There is no evidence in his writing of the exciting developments in oil painting taking place in the early 15th century. This suggests that his book was indeed written sometime in the 14th century.

Cennini's intention was to provide a practical handbook for the apprentice painter. Along with technical methods, Cennini offered advice on the sort of lifestyle to which a young painter should subscribe. "Your life should be arranged just as if you were studying theology, or philosophy, or other theories, that is to say, eating and drinking moderately, at least twice a day, electing digestible and wholesome dishes, and light wines; saving and sparing your hand, preserving it from such strains as heaving stones, crowbars, and many other things which are bad for your hand, from giving them a chance to weary it. There is another cause which, if you indulge it, can make your hand so unsteady that it will waver more, and flutter far more, than leaves do in the wind, and this is indulging too much in the company of women."

According to Victoria Finlay, in her book Colour: Travels Through The Paintbox, the infamous UK forger Eric Hebborn was greatly influenced by Cennino Cennini. The last book Hebborn wrote before he was brutally murdered was The Art Forger's Handbook. Finlay writes that he "used and adapted Cennino's advice extensively - preparing panels, tinting papers different colours, and making brand new works look as if they had been varnished some time before (by beating egg-white, left overnight and then painted on with a brush), just as the master advised."

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Coloured Gold

While pure gold is yellow in colour, coloured gold can be developed into various colours. These colours are generally obtained by alloying gold with other elements in various proportions.

For example, alloys which are mixed 14 parts gold to 10 parts alloy create 14-karat gold, 18 parts gold to 6 parts alloy creates 18 karat, and so on. This is often expressed as the result of the ratio, i.e.: 14/24 equals 0.585 and 18/24 is 0.750. There are hundreds of possible alloys and mixtures, but in general the addition of silver will colour gold white, and the addition of copper will colour it red. A mix of around 50/50 copper and silver gives the range of yellow gold alloys the public is accustomed to seeing in the marketplace. A small amount (0.2%) of zinc can be added to harden the alloy.

The most common grades of gold, in addition to pure 24K, are 22K (92%), 18K (75%), 14K (58%) and 9K (38%).

Coloured gold can be classified to three groups:

the Au-Ag-Cu system, producing white, yellow, green and red golds; typically malleable alloys
the intermetallic compounds, producing blue and purple golds, as well as other colours. These are typically brittle but can be used as gems and inlays
the surface oxide layers, such as black gold; mechanical properties depend on the bulk alloy, and the coloured surface is prone to wear

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White gold is an alloy of gold and at least one white metal, usually nickel, manganese or palladium. Like yellow gold, the purity of white gold is given in karats.

White gold's properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for many different purposes; while a nickel alloy is hard and strong and therefore good for rings and pins, gold-palladium alloys are soft, pliable and good for white gold gemstone settings, sometimes with other metals like copper, silver, and platinum for weight and durability, although this often requires specialized goldsmiths. The term white gold is used very loosely in the industry to describe karat gold alloys with a whitish hue. Many believe that the color of the rhodium plating, which is seen on many commercial pieces, is actually the color of white gold. The term "white" covers a large spectrum of colors that borders or overlaps pale yellow, tinted brown, and even very pale rose. The jewelry industry often hides these off-white colors by rhodium plating.

A common white gold formulation consists of 90 wt.% gold and 10 wt.% nickel. Copper can be added to increase malleability.

The strength of gold-nickel-copper alloys is caused by formation of two phases, a gold-rich Au-Cu, and a nickel-rich Ni-Cu, and the resulting hardening of the material.

The alloys used in jewelry industry are gold-palladium-silver and gold-nickel-copper-zinc. Palladium and nickel act as primary bleaching agents for gold; zinc acts as a secondary bleaching agent to attenuate the color of copper.

About one out of eight people have an allergic reaction to the nickel in some white gold alloys when worn over long periods. A typical reaction is a minor skin rash. Because of this, many European countries do not use nickel white gold. White gold alloys made without nickel are less likely to be allergenic.

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Rose gold is a gold and copper alloy widely used for specialized jewelry. It is also known as pink gold and red gold. As it was popular in Russia at the beginning of the nineteenth century, it is also known as Russian gold, although this term has become somewhat rare.

Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content – the higher the copper content, the stronger the red coloration. A common alloy for rose gold is 75% gold and 25% copper by mass (18 karat). Since rose gold is an alloy, there is no such thing as "pure rose gold".

A common formulation for red gold is 50% gold and 50% copper.

Up to 15% zinc can be added to copper-rich alloys to change their colour to reddish yellow or dark yellow.

The highest karat version of rose gold is also known as crown gold, which is 22 karat. Eighteen karat red gold may be made of 25% copper and 75% gold. For 18 karat rose gold, typically about 4% silver is added to 75% gold and 21% copper to give a rose colour. 14 karat red gold is often found in the Middle East and contains 41.67% copper.

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Spangold Some gold-copper-aluminum alloys form a fine surface texture at heat treatment, yielding an interesting spangling effect. At cooling, they undergo a quasi-martensitic transformation from body-centered cubic to body-centered tetragonal phase; the transformation does not depend on the cooling rate. A polished object is heated in hot oil to 150-200 °C for 10 minutes then cooled below 20 °C, forming a sparkly surface covered with tiny facets.

The alloy of 76% gold, 19% copper, and 5% aluminum yields yellow colour, the alloy of 76% gold, 18% copper and 6% aluminum is pink.

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Green gold alloys are made by leaving the copper out of the alloy mixture and just using gold and silver. It actually appears as a greenish yellow rather than green. Eighteen karat green gold would therefore contain a mix of gold 75% and silver 25% (or 73% gold and 27% silver). Fired enamels adhere better to these alloys.

Green gold was known to Lydians as long ago as 860 BC under the name electrum. Electrum is a naturally occurring alloy of silver and gold.

Cadmium can be added to gold alloys in amount of up to 4% to achieve green color. The alloy of 75% gold, 23% copper, and 2% cadmium yields light green 18ct gold. The alloy of 75% gold, 15% silver, 6% copper, and 4% cadmium yields a dark green alloy. Cadmium is, however, toxic.

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Grey gold alloys are made by adding silver, manganese and copper in specific ratios to the gold.

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Black gold is a type of gold used in jewelry. Black colored gold can be produced by various methods:

Electroplating, using black rhodium or ruthenium. Solutions that contain ruthenium give a slightly harder black coating than those that contain rhodium.
Patination by applying sulfur and oxygen containing compounds.
Plasma assisted chemical vapor deposition process involving amorphous carbon
Controlled oxidation of gold containing chromium or cobalt (e.g. 75% gold, 25% cobalt).

A range of colors from brown to black can be achieved on copper-rich alloys by treatment with potassium sulfide.

Cobalt-containing alloys, e.g. 75% gold with 25% cobalt, form a black oxide layer with heat treatment at 700-950 °C. Copper, iron and titanium can be also used for such effect. Gold-cobalt-chromium alloy (75% gold, 15% cobalt, 10% chromium) yields surface oxide that's olive-tinted because of the chromium(III) oxide content, is about 5 times thinner than Au-Co and has significantly better wear resistance. The gold-cobalt alloy consists of a gold-rich (about 94% Au) and cobalt-rich (about 90% Co) phases; the cobalt-rich phase grains are capable of oxide layer formation on their surface.

More recently a laser technique has been developed that renders the surface of metals deep black. A femtosecond laser pulse deforms the surface of the metal forming nanostructures. The immensely increased surface area can absorb virtually all the light that falls on it thus rendering it deep black.

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Purple gold (also called amethyst gold and violet gold) is an alloy of gold and aluminum rich in gold-aluminium intermetallic (AuAl₂). Gold content in AuAl₂ is around 79% and can therefore be referred to as 18 karat gold. Purple gold is more brittle than other gold alloys, as it is an intermetallic compound instead of a malleable alloy, and a sharp blow may cause it to shatter. It is therefore usually machined and faceted to be used as a "gem" in conventional jewelry rather than by itself. At lower content of gold, the material is composed of the intermetallic and an aluminium-rich solid solution phase. At higher content of gold, the gold-richer intermetallic AuAl forms; the purple color is preserved to about 15% of aluminium. At 88% of gold the material is composed of AuAl and changes color. (The actual composition of AuAl₂ is closer to Al₁₁Au₆ as the sublattice is incompletely occupied.)

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Blue gold is an alloy of gold and indium. It contains 46% gold (about 12 ct) and 54% indium, forming an intermetallic compound AuIn₂, with a clear blue color. With gallium, gold forms an intermetallic AuGa₂ (58.5% Au, 14ct) which has slight bluish hue. The melting point of AuIn₂ is 541 °C, for AuGa₂ it is 492 °C. AuIn₂ is less brittle than AuGa₂, which itself is less brittle than AuAl₂.

All the AuX₂ intermetallics have crystal structure of CaF₂ and therefore are brittle. Deviation from the stoichiometry results in loss of color. Slightly nonstoichiometric compositions are however used, to achieve a fine-grained two- or three-phase microstructure with reduced brittleness. A small amount of palladium, copper or silver can be added to achieve a less brittle microstructure.

The intermetallic compounds tend to have poor corrosion resistance. The less noble elements are leached to the environment, and a gold-rich surface layer is formed. Direct contact of blue and purple gold elements with skin should be avoided as exposition to sweat may result in metal leaching and discoloration of the metal surface.

A surface plating of blue gold on karat gold or sterling silver can be achieved by a gold plating of the surface, followed by indium plating, with layer thickness matching the 1:2 atomic ratio. A heat treatment then causes interdiffusion of the metals and formation of the required intermetallic compound.

Blue gold can be achieved by formation of an oxide layer on an alloy of 75% gold, 24.4% iron, and 0.6% nickel; the layer forms on heat treatment in air between 450–600 °C.

Gold of purity 20–23 carat, when alloyed with ruthenium, rhodium and three other elements and heat-treated at 1800 °C, forms a 3–6 micrometers thick surface layer with a rich sapphire blue color.

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Copper

Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys.

The metal and its alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of Cyprus), later shortened to сuprum. Its compounds are commonly encountered as copper(II) salts, which often impart blue or green colors to minerals such as turquoise and have been widely used historically as pigments. Architectural structures built with copper corrode to give green verdigris. Decorative art prominently features copper, both by itself and as part of pigments.

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Denatured alcohol

Denatured alcohol (or methylated spirits) is ethanol that has additives to make it more poisonous or unpalatable, and thus, undrinkable. In some cases it is also dyed.

Denatured alcohol is used as a solvent and as fuel for spirit burners and camping stoves. Because of the diversity of industrial uses for denatured alcohol, hundreds of additives and denaturing methods have been used. Traditionally, the main additive is 10% methanol, giving rise to the term 'methylated spirit'. Other typical additives include isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and denatonium. Denaturing alcohol does not chemically alter the ethanol molecule. Rather, the ethanol is mixed with other chemicals to form an undrinkable mixture. Different additives are used to make it difficult to use distillation or other simple processes to reverse the denaturation. Methanol is commonly used both because of its boiling point being close to that of ethanol and because it is toxic. In many countries, it is also required that denatured alcohol be dyed blue or purple with an aniline dye.

As a sanding aid, as the alcohol helps to more easily remove excess dust because it does not open the wood grain the way that water does.As a solvent in shellac and shellac-based products.

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Ductility

Ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature.

A material's ductility and malleability are not always coextensive. For instance, while gold is both ductile and malleable, lead is only malleable. The word ductility is sometimes used to embrace both types of plasticity.

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Dutch metal

Dutch metal is a form of brass being an alloy of copper, 84% and zinc 16%. It is very malleable and ductile and can be beaten into very thin sheets. It is these sheets that are sold as Dutch Metal, for use as metal leaf or imitation gold leaf. The addition of arsenic produces an alloy with similar properties but coloured white.

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Embossing

Embossing is a process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female dies, or by passing sheet or a strip of metal between rolls of the desired pattern. Embossing has the characteristics to form ductile metals. It is used in production runs and maintains the same metal thickness before and after embossing. Unlimited patterns can be produced or patterns with no varaition.

Metals commonly embossed are: Aluminium, Brass, Copper, Galvanized steel, Steel (All Alloys), and Zinc.

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Enamel paint

Enamel paint is paint that air dries to a hard, usually glossy, finish, used for coating surfaces that are outdoors or otherwise subject to hard wear or variations in temperature; it should not be confused with decorated objects in "painted enamel", where vitreous enamel is applied with brushes and fired in a kiln. The name is something of a misnomer as in reality, most commercially-available enamel paints are significantly softer than either vitreous enamel or stoved synthetic resins, and are totally different in composition; vitreous enamel is applied as a powder of paste and then fired at high temperature. There is no generally accepted definition or standard for use of the term enamel paint, and not all enamel-type paints may use it.

Typically the term "enamel paint" is used to describe oil-based covering products, usually with a significant amount of gloss in them, however recently many latex or water-based paints have adopted the term as well. The term today means "hard surfaced paint" and usually is in reference to paint brands of higher quality, floor coatings of a high gloss finish, or spray paints. Some enamel paints have been made by adding varnish to oil-based paint.

Floor enamel – May be used for concrete, stairs, basements, porches, and patios.
Fast dry enamel – Can dry within 10–15 minutes of application. Ideal for refrigerators, counters, and other industrial finishes.
High-temp enamel – May be used for engines, brakes, exhaust, and BBQs.
Enamel paint is also used on wood to make it resistant to the elements via the waterproofing and rot-proofing properties of enamel. Generally, treated surfaces last much much longer and are much more resistant to wear than untreated surfaces.
Model building - This paint is usually sold in 14 ml tinlets.

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Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a powerful psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a solvent, and as a fuel. In common usage, it is often referred to simply as alcohol or spirits.

Ethanol is miscible with water and is a good general purpose solvent. It is found in paints, tinctures, markers, and personal care products such as perfumes and deodorants. It may also be used as a solvent in cooking, such as in vodka sauce.

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Foil

Foil is a very thin sheet of metal, usually made by hammering or rolling a piece of metal. Foils are most easily made with malleable metals, such as aluminium, copper, tin, and gold. Foils usually bend under their own weight and can be torn easily. The more malleable a metal, the thinner foil can be made with it. For example, aluminium foil is usually about 1/1000 inch (0.03 mm), whereas gold (more malleable than aluminium) can be made into foil only a few atoms thick. Such extremely thin foil is called leaf. Leaf tears very easily and must be picked up with special brushes.

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Gesso

Gesso (from the Latin gypsum) is a white paint mixture consisting of a binder mixed with chalk, gypsum, pigment, or any combination of these. It is used in artwork as a preparation for any number of substrates such as wood panels, canvas and sculpture as a base for paint and other materials that are applied over it.

"Gesso", also known "glue gesso" or "Italian gesso" is a traditional mix of an animal glue binder, usually rabbit-skin glue, chalk, and white pigment, used to coat rigid surfaces such as wooden painting panels as an absorbent primer coat substrate for painting. Its absorbency makes it work with all painting media including water-based media, different types of tempera, and oil paint. It is also used as a base on three-dimensional surfaces for the application of paint or gold leaf. Mixing and applying it is an art form in itself since it is usually applied extremely thin in 10 layers or more. It is a permanent and brilliant white substrate, used on wood, masonite and other surfaces. The standard hide glue mixture is rather brittle and susceptible to cracking, thus making it suitable for rigid surfaces only. For priming flexible canvas, a emulsion of gesso and linseed oil, also called a "half-chalk ground", is used. In Geology, Italian "Gesso" corresponds to the English "Gypsum", as it is a calcium sulphate compound (CaSO₄·2H₂O).

Modern "acrylic gesso" is technically not gesso at all. It is a combination of calcium carbonate with an acrylic polymer medium latex, a pigment and other chemicals that ensure flexibility, and ensure long archival life. It is sold premixed for both sizing and priming a canvas for painting. While it does contain calcium carbonate (CaCO3) to increase the absorbency of the primer coat, Titanium dioxide or titanium white is often added as the whitening agent. This allows the "gesso" to remain flexible enough to use on canvas. High concentrations of calcium carbonate, or substandard latex components will cause the resulting film to dry to a brittle surface susceptible to cracking.

Acrylic gesso can be coloured, either commercially by replacing the titanium white with another pigment, such as carbon black, or by the artist directly, with the addition of an acrylic paint. Acrylic gesso can be odorous, due to the presence of ammonia and/or formaldehyde which are added in small amounts as preservatives against spoilage. Pre-gessoed canvases can be obtained commercially.

Acrylic gesso is a modern art material, and is used as a primer for oil painting and acrylics. Many of the solvents used in oil painting, such as turpentine or odorless mineral spirits (OMS), will leach some oil through a thin acrylic primer coat and damage the canvas underneath just as traditional hide glue sizing did. However, sufficient coverage and penetration of an absorbent support is archivally acceptable.

Although it is generally believed to be acceptable, several painting texts such as The Painter's Handbook state that it is unwise to paint in oils over acrylic gesso because, unlike with time-tested alternatives such as rabbit skin glue, the oil paint will eventually delaminate from the acrylic gesso surface. This effect may not make itself manifest for several decades. The cause for this problem is the inability of oil paint to establish both physical and chemical bonds with the acrylic base. Applied to a canvas that has been primed with rabbit-skin glue, oil paint is able to penetrate the ground (which is porous, unlike acrylic gesso) and establish a permanent bond, both chemical and physical. Manufacturers of commercially sold, pre-gessoed canvases deny that delamination takes place. However, curators in the Smithsonian Museum are not permitted to use acrylic gesso under oil paint, precisely because of the delamination problem.

Soy-based gesso is a low emitting bio-based gesso made from recycled soy content. Soy gesso is made with new bio-based dispersion technology that uses a soy ester with a modified soy-vegetable oil acrylic. The surface is similar to acrylic gesso, but is not a solid acrylic. Soy gesso is made using a thin film of a modified acrylic and the soy ester. The penetration and adhesion of the soy ester to the substrate and the thin film of modified acrylic may have advantages in creating a surface that allows a physical bond between the gesso and the oil paint. In addition, the thinner modified acrylic film is less resistant to cracking than a solid acrylic gesso.

Gesso is also used by sculptors to prepare the shape of the final sculpture (fused bronze) or directly as a material for sculpting. Gesso can also be used as a layer between sculptured wood and gold leaf. In this case, a layer of red shellac called "assiette" is used to cover the Gesso before applying the gold. A collection of gesso sculptures is properly called a gypsotheque.

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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 glueing, chemical gilding, and electroplating, the last also called gold plating.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.

Herodotus mentions that the Egyptians gilded wood and metals, and many such objects have been excavated. Certain Ancient Greek statues of great prestige were chryselephantine, 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 of Carthage, 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).

In Europe, silver-gilt has always been more common than gilt-bronze, but in China the opposite has been the case. The medieval Chinese also developed the gilding of porcelain, which was later taken up by the French and other European potters.

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 framemaking 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.

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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 paperstainer 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 burnisher, 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), 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 was 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.

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Chemical Gilding

Chemical gilding embraces those processes in which the gold is at some stage of chemical combination. These include:

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 electroless 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.

When the metal to be gilded is wrought or chased, it ought to be covered with mercury before the amalgam is applied, that this may be more easily spread; but when the surface of the metal is plain, the amalgam may 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.

The amalgam being equally spread over the prepared surface of the metal, the mercury is then sublimed by a heat just sufficient for that purpose; for, if it is too great, part of the gold may be driven off, or it may run together and leave some of the surface of the metal bare. When the mercury has evaporated, which is known by the surface having entirely become of a dull yellow colour, the metal must undergo other operations, by which the fine gold colour is given to it. 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 colour of the gilding is heightened, and the effect seems to be produced by a perfect dissipation of some mercury remaining after the former operation. The dissipation is well effected by this equable application of heat. 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 thus covered is exposed to heat, and then quenched in water.

By this method its colour 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, but owing to the exposure of the workmen to mercurial fumes, it is very unhealthy. There is also much loss of mercury to the atmosphere, which brings extremely serious environmental concerns as well.

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 neurological damage and endocrine disorders, since inhalation is a very efficient route for mercuric compounds to enter the body. This process has generally been supplanted by the electroplating of gold over a nickel substrate, which is more economical and less dangerous.

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Depletion gilding

Depletion gilding is a method for producing a layer of nearly pure gold on an object made of gold alloy by removing the other metals from its surface. It is sometimes referred to as a "surface enrichment" process.

Process

Most gilding methods are additive, that is, they deposit gold that was not there before onto the surface of an object. By contrast, depletion gilding is a subtractive process whereby material is removed to increase the purity of gold that is already present on an object's surface.

Essentially, depletion gilding produces a high-purity gold surface by removing everything that is not gold. More specifically, other metals are etched away from the surface of an object composed of a gold alloy by the use of acids or salts, often in combination with heat. Of course, since no gold is actually added, only an object made of an alloy that already contains at least some gold can be depletion gilded.

Depletion gilding relies on the fact that gold is highly resistant to oxidation or corrosion by most common chemicals, whereas many other metals are not. Depletion gilding is most often used to treat alloys of gold with copper and/or silver. Unlike gold, both copper and silver readily react with a variety of chemicals. For example, nitric acid is effective as an etching agent for both copper and silver. Under the proper circumstances, even ordinary table salt (sodium chloride) will react with either metal.

The object to be gilded is coated, immersed, or packed in a suitable acid or salt. These chemicals then attack the metallic copper and silver in the object's surface, transforming it to various copper and silver compounds. The object is usually heated to make the etching process more efficient. Regardless, the resulting copper and silver compounds can be removed from the object's surface by a number of processes. Washing, chemical leaching, heating, or even physical absorption by porous materials such as brick dust have all been used. However, the relatively inert gold remains behind, unaffected. The result is a thin layer of nearly pure gold on the surface of the original object.

There is no well-defined minimum gold content required to successfully depletion gild an object. However as a practical matter, the less gold that is present, the more other material must be etched away to produce the desired surface appearance. In addition, the removal of the other metals usually leaves the surface covered with microscopic voids and pits. This can make the surface soft and "spongy" with a dull or matte appearance. This effect becomes more pronounced as more base metal is removed. For this reason, most depletion gilded objects are burnished to make their surfaces more durable and give them a more attractive polished finish.

Like other gilding processes, depletion gilding provides a way to produce the appearance of pure gold without its disadvantages. Most obviously, the cost and rarity of gold limits the use of the pure metal, especially in large objects. In addition, pure gold is both extremely soft and very dense, two factors that limit its utility. By producing a layer of gold over a layer of copper or other metal, objects can be made that are lighter, sturdier, and cheaper while still appearing to be nearly pure gold.

The term depletion gilding usually refers to the production of a layer of gold. However, it can also be used to produce a layer that is an alloy of gold and silver, sometimes referred to as electrum. Certain chemicals, such as oxalic acid, attack copper but do not affect either silver or gold. Using such a chemical, it is possible to remove only the copper in an alloy, leaving both silver and the gold behind. Thus, if the original object is composed of copper, silver, and gold, it can be given a gold surface by removing both silver and copper, or an electrum surface by removing only the copper.

Likewise, with an appropriate chemical, a layer of nearly pure silver can be produced on an object made of copper and silver. For instance, sterling silver can be depleted - 'depletion silvering' - to produce a fine silver surface, perhaps as preamble to application of gold, as in the Keum-boo technique.

However, in the majority of cases depletion gilding is in fact used to produce a gold finish, rather than one of electrum or silver.

Depletion gilding is a decorative process, with no significant industrial applications. It is not widely used in modern times, having been superseded by processes more suited to mass production, such as electroplating. Some individual artisans and small shops continue to practice it.

However, depletion gilding was widely used in antiquity. While it requires skill to execute it well, the process itself is technologically simple, and uses materials that are readily available to most ancient civilizations. Some form of depletion gilding has been used by nearly every culture that developed metalworking. The South American Sican culture in particular developed depletion gilding to a high art. Some ancient alloys, such as tumbaga, may have been developed specifically for use in depletion gilding.

Certain cultures are thought to have attached mythical or spiritual significance to the process. Gold was considered sacred in many early civilizations and was highly valued in nearly all of them, and anything relating to it had the potential to take on cultural importance. Moreover, the ability to turn what appeared to be an object made of copper into what seemed to be pure gold would be very impressive. There is some speculation that depletion gilding may have contributed to the concepts of alchemy, a major goal of which was to physically transform one metal into another.

Gilding of 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. 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 permanence. 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.

A number of different forms and compositions are available to apply gold to ceramic, and these include:

Acid Gold - developed in 1860s at Mintons, Stoke-on-Trent, England. The glazed surface is etched with dilute hydrofluoric acid prior to application of the gold; the process demands great skill and is used for the decoration only of ware of the highest class.
Bright Gold or Liquid Gold - is a solution of gold sulphoresinate together with other metal resinates and a bismuth-based flux. It is particularly bright when drawn from the decorating kiln and so needs little further processing.
Burnish Gold or Best Gold - is applied to the ware as a suspension of gold powder in essential oils mixed with lead borosilicate or a bismuth-based flux. This type of gold decoration is dull as taken from the kiln and requires burnishing, usually with agate, to bring out the colour. As the name suggests it is considered the highest quality of gold decoration. One solvent-free burnish gold composition was reported to consist of 10 to 40% gold powder, 2 to 20% polyvinylpyrrolidone, 3 to 30% an aqueous acrylate resin and 5 to 50% water.

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Gold Leaf

Gold leaf is gold that has been hammered into extremely thin sheets and is often used for gilding. Gold leaf is available in a wide variety of karats and shades.

Gold leaf is sometimes confused with metal leaf but they are different products. The term metal leaf is normally used for thin sheets of metal of any colour that do not contain any real gold.

Gold leaf has traditionally been most popular and most common in its use as gilding material for decoration of art (including statues and Eastern Christian icons) or the picture frames that are often used to hold or decorate paintings, mixed media, small objects (including jewelry) and paper art. "Gold" frames made without leafing are also available for a considerably lower price, but traditionally some form of gold or metal leaf was preferred when possible and gold leafed (or silver leafed) moulding is still commonly available from many of the companies that produce commercially-available moulding for use as picture frames.

The manufacture of gold leaf is a craft with 5000 years of history and tradition. During the reign of the Pharaohs, craftsmen beat gold leaf to a thickness similar to our modern product. Gilded objects in Cairo's Egyptian Museum reveal that the most superior methods known to us, including the use of water gilding, has been mastered by these early gilding artisans. A gold nugget of 5 mm in diameter (bottom) can be expanded through hammering into a gold foil of about 0.5 square meter.

Gold leaf is manufactured from an alloy of gold, silver and copper. At the start of the manufacturing process, the metals are melted at 1250 °C, cast into a bar and rolled out into a thin ribbon. In the first beating process, called the "shodder", the ready laminated ribbon is cut into squares measuring 40 x 40 mm, these are interleaved and beaten out to 160 x 160 mm with hammers. In the second beating process, called the "mould", the finished beaten shodder gold is again cut into squares, interleaved and subsequently beaten out to the final thickness of 0.000125 mm. The finished gold leaf is removed from the mould by hand, checked carefully for possible flaws, cut into a standard square or rectangle and inserted into paper booklets. A standard size is a square leaf of 85mm. Each leaf can therefore cover a maximum of 72 cm² and an entire booklet of 25 leaves will cover approximately 0.42 m² or 1 ft 6 in².

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Gold Plating

Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver (to make silver-gilt), by chemical or electrochemical plating. This article covers plating methods used in the modern electronics industry; for more traditional methods, often used for much larger objects, see gilding.

Gold plating of silver is used in the manufacture of jewelry. Like copper, silver atoms diffuse into the gold layer, causing slow gradual fading of its colour and eventually causing tarnishing of the surface. This process may take months and even years, depending on the thickness of the gold layer. A barrier metal layer is used to counter this effect. Copper, which also migrates into gold, does so more slowly than silver. The copper is usually further plated with nickel. A gold-plated silver article is usually a silver substrate with layers of copper, nickel, and gold deposited on top of it.

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Investment casting

Investment Casting is an industrial process based on and also called lost-wax casting, one of the oldest known metal-forming techniques. From 5,000 years ago, when beeswax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the production of components with accuracy, repeatability, versatility and integrity in a variety of metals and high-performance alloys. Lost foam casting is a modern form of investment casting that eliminates certain steps in the process.

The process is generally used for small castings, but has been used to produce complete aircraft door frames, steel castings of up to 300 kg (660 lbs) and aluminium castings of up to 30 kg (66 lbs). It is generally more expensive per unit than die casting or sand casting, but has lower equipment costs. It can produce complicated shapes that would be difficult or impossible with die casting, yet like that process, it requires little surface finishing and only minor machining.

The history of lost-wax casting dates back thousands of years. Its earliest use was for idols, ornaments and jewellery, using natural beeswax for patterns, clay for the moulds and manually operated bellows for stoking furnaces. Examples have been found across the world in India's Harappan Civilisation (2500–2000 BC) idols, Egypt's tombs of Tutankhamun (1333–1324 BC), Mesopotamia, Aztec and Mayan Mexico, and the Benin civilization in Africa where the process produced detailed artwork of copper, bronze and gold.

The earliest known text that describes the investment casting process (Schedula Diversarum Artium) was written around 1100 A.D. by Theophilus Presbyter, a monk who described various manufacturing processes, including the recipe for parchment. This book was used by sculptor and goldsmith Benvenuto Cellini (1500–1571), who detailed in his autobiography the investment casting process he used for the Perseus with the Head of Medusa sculpture that stands in the Loggia dei Lanzi in Florence, Italy.

Investment casting came into use as a modern industrial process in the late 19th century, when dentists began using it to make crowns and inlays, as described by Dr. D. Philbrook of Council Bluffs, Iowa in 1897. Its use was accelerated by Dr. William H. Taggart of Chicago, whose 1907 paper described his development of a technique. He also formulated a wax pattern compound of excellent properties, developed an investment material, and invented an air-pressure casting machine.

In the 1940s, World War II increased the demand for precision net shape manufacturing and specialized alloys that could not be shaped by traditional methods, or that required too much machining. Industry turned to investment casting. After the war, its use spread to many commercial and industrial applications that used complex metal parts.

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Karat

The karat (abbreviation kt) is a measure of the purity of gold alloys, 24 karat being pure gold.

The karat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity of precious metals is denoted by parts per thousand of pure metal in the alloy.

The most common karats used for gold in bullion, jewelry making and by goldsmiths and gilders are:

24 karat (millesimal fineness 999 or higher)
22 karat (millesimal fineness 916)
21 karat (millesimal fineness 875)
20 karat (millesimal fineness 833)
18 karat (millesimal fineness 750)
15 karat (millesimal fineness 625)
14 karat (millesimal fineness 585)
10 karat (millesimal fineness 417)
9 karat (millesimal fineness 375)
8 karat (millesimal fineness 333)
1 karat (millesimal fineness 042)

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Lost-Wax Casting

In lost-wax or investment casting, the artist starts with a full-sized model of the sculpture, most often a non-drying oil-based clay such as Plasticine model for smaller sculptures or for sculptures to be developed over an extended period (water-based clays must be protected from drying), and water-based clay for larger sculptures or for sculptures for which it is desired to capture a gestural quality - one that transmits the motion of the sculptor in addition to that of the subject. A mold is made from the clay pattern, either as a piece mold from plaster, or using flexible gel or similar rubber-like materials stabilized by a plaster jacket of several pieces. Often a plaster master will be made from this mold for further refinement. Such a plaster is a means of preserving the artwork until a patron may be found to finance a bronze casting, either from the original molds or from a new mold made from the refined plaster positive.

Once a production mold is obtained, a wax (hollow for larger sculptures) is then cast from the mold. For a hollow sculpture, a core is then cast into the void, and is retained in its proper location (after wax melting) by pins of the same metal used for casting. One or more wax sprues are added to conduct the molten metal into the sculptures - typically directing the liquid metal from a pouring cup to the bottom of the sculpture, which is then filled from the bottom up in order to avoid splashing and turbulence. Additional sprues may be directed upward at intermediate positions, and various vents may also be added where gases could be trapped. (Vents are not needed for ceramic shell casting, allowing the sprue to be simple and direct.) The complete wax structure (and core, if previously added) is then invested in another kind of mold or shell, which is heated in a kiln until the wax runs out and all free moisture is removed. The investment is then soon filled with molten bronze. The removal of all wax and moisture prevents the liquid metal from being explosively ejected from the mold by steam and vapor.

Students of bronze casting will usually work in direct wax, where the model is made in wax, possibly formed over a core, or with a core cast in place, if the piece is to be hollow. If no mold is made and the casting process fails, the artwork will also be lost. After the metal has cooled, the external ceramic/clay is chipped away, revealing an image of the wax form, including core pins, sprues, vents, and risers. All of these are removed with a saw and tool marks are polished away, and interior core material is removed to reduce the likelihood of interior corrosion. Incomplete voids created by gas pockets or investment inclusions are then corrected by welding and carving. Small defects where sprues and vents were attached are filed or ground down and polished.

For a large sculpture, the artist will usually prepare small study models until the pose and proportions are determined. An intermediate-sized model is then constructed with all of the final details. For very large works, this may again be scaled to a larger intermediate. From the final scale model, measuring devices are used to determine the dimensions of an armature for the structural support of a full-size temporary piece, which is brought to rough form by wood, cardboard, plastic foam, and/or paper to approximately fill the volume while keeping the weight low. Finally, plaster, clay or other material is used to form the full-size model, from which a mould may be constructed. Alternatively, a large refactory core may be constructed, and the direct-wax method then applied for subsequent investment. Before modern welding techniques, large sculptures were generally cast in one piece with a single pour. Welding allows a large sculpture to be cast in pieces, then joined.

After final polishing, corrosive materials may be applied to form a patina, a process that allows some control over the colour and finish.

Another form of sculptural art that uses bronze is ormolu, a finely cast soft bronze that is gilded (coated with gold) to produce a matte gold finish. Ormolu was popularized in the 18th century in France and is found in such forms as wall sconces (wall-mounted candle holders), inkstands, clocks and garnitures. Ormolu wares can be identified by a clear ring when tapped, showing that they are made of bronze, not a cheaper alloy such as spelter or pewter.

Nimbus

Nimbus is the luminous disk or circle or other indication of light around the head of a sacred personage. It was used in Buddhist and other Asian art and by the early Greeks and Romans to designate gods and heroes. Christian art from the 5th cent. usually a circle or disk, the nimbus has various forms—triangular for God the Father; a circle with a cross for Jesus; a square for a living person; a disk or circle for a saint, with sometimes a band of small stars for the Virgin Mary. In stained glass figures were often represented surrounded by an ovoid light called a vesica piscis [Lat.,=fish bladder]. The square form was symbolic of the material world; the circle symbolized spiritual perfection and eternal blessedness; and the triangle represented eternity and the Trinity. The nimbus is usually of gold and may have a clearly defined outline or the light may be diffused, radiating from the head in lines that melt into the picture. The term aureole may denote a crown or radiance around the head or it may be an oval used as a background for the whole body. When nimbus and aureole are combined for one figure, the illumination is called a glory. An almond-shaped glory is a mandorla. Halo is a nontechnical term to denote either a disk behind the head or a circle surrounding it.

investment casting

water color

chryselephantine

furniture polish

mercury

lead

zinc

tin

arsenic, phosphorus, aluminum, manganese, and silicon, (see brass)

nickel

palladium

tarnish

sculptures

ceramic

marble sculpture

plasticine

patina

spelter

copper alloy

list of copper alloys

substrate (see burnishing

precious metal

bullion

carat weight

goache

pigments

brushes

rhodium

ruthenium

crown gold

vitreous enamel

electrum

cadmium

oxidise

chromium (see black gold)

cobalt (see black gold)

potassium sulphide (see black gold)

indium (see blue gold)

turquoise

mallachite

verdigris

decorative art

Malleability (see Ductility)

sizing

gypsotheque

silver gilt

gilt-bronze

electoplating

gold-plating

ammonia