Gilding

As Gilding refers to the coating of metallic and non-metallic objects with gold, gold alloys and other decorative metal layers.

The traditional craft of the gilder is to apply sheet metal on workpieces, in contrast with their coating with metallic effect pigment ( Shell gold, " gold bronze "), which is part of the craft of the painter. The chemical methods with the exception of fire gilding developed only in modern times.

Gold is not only of noble appearance, but also one of the most corrosion-resistant metals. In its pure form it is for components and everyday objects ill-suited because it is rare and expensive and has a low strength. The coating readily available and suitable for everyday use materials with a layer of gold is valued since ancient times.

Base materials

The most important group of materials which are particularly well suited for gilding are metals and metal alloys, especially steel, stainless steel, zinc, brass, bronze, copper, silver and many more. To non -metallic materials such as porcelain, glass, ceramics, wood, paper, leather, plastic and even gold-plated textiles in rare cases.

Meanwhile, you can gild almost all organic and inorganic materials on a permanent thanks to the latest technology. This is done through new methods in electroplating.

Functions

Historically, the most important functions of gold films and coatings:

• Decorative appearance
• Valuable and prestigious appearance
• Importance for cults and religion
• Corrosion resistance

In modern times, nor were added the following features:

• With gold-plated electrical contacts and plugs a small foreign film resistor
• Special properties for the semiconductor, for example bondability

Gold coatings

Gold coatings can be made of pure gold, in most cases suitable for the particular purpose gold alloy is used as coating material but chosen. The gold alloys differ in color: red gold, yellow gold, white gold and rose. Also, green and blue colors are available. The colors are achieved by the following alloying elements: copper for rose gold, silver, cadmium, and zinc for yellow to white gold, nickel for white gold and indium for Blue Gold.

Important when the color is, the hardness and wear resistance of the coating for industrial applications. These properties are largely improved by the alloying elements iron, cobalt and nickel. Such a gold coating called hard gold. The alloying elements to improve hardness and wear resistance. The saved amount of gold, however, is negligible.

Method

The two basic techniques of gilding are the mechanical and the chemical procedure. The mechanical plating types are the oldest method; besides, gold plate was flattened. A distinction between gloss and matt gilding, water gilding, oil gilding, Mordentvergoldung and rear glass gilding. The chemical gilding originated with the exception of fire gilding until much later. With the electroplating chemical gilding peaked.

When gilding a craft operation is called, the primarily engaged in the processing of wood, metal or plastic surfaces.

Gold leaf

In the painting, especially in panel painting, the application of gold leaf is referred to a substrate as gilding. This surface can be designed differently. In the book painting may have been deposited directly on the parchment or on a gold background gold; this reason gold is found in the panel painting mostly. It is a primer ( gilding ), which always consists of a bolus ( pigment) and a binder.

In the art of forging have been used for many centuries quality work, such as grids, church furnishings, grave crosses, etc. usually through the ironwork itself, accentuated color with gold leaf or gold plated over the entire surface. The weather-resistant oil gilding with Mixtion or applying oil will be used.

Electrochemical cementation

Carbonization is because the immersion, for example, a copper sheet into a gold (III ) chloride solution the nobler gold ions are reduced and deposited on the surface of the copper, in which copper is oxidized to be copper ( II) ions.

Here, the copper surface but must previously well cleaned or etched, and the solution slightly alkaline. After the deposition of gold in a layer of a few micrometers can increase the adhesion when the article is heated at temperatures of about 700 ° C, with a diffusion zone is formed between the copper and the gold layer.

The process of cementation is already known from the metallurgy of pre-Columbian Andean culture. To prepare the gold chloride solution probably gold foils were dissolved in a hot solution of potassium aluminum sulfate, potassium nitrate and sodium chloride, but this took several days to complete.

Galvanic processes

Most gold coatings are applied by electroplating method. This method has many older techniques based completely. The usually metallic articles being immersed in an electrolyte and gold by applying a dc electric voltage to a gold coating is deposited. The first patent for the separation of gold from cyanide baths was granted in 1840 to George Richards Elkington and Henry Elkington.

During the electroplating method, gold (I) - or gold ( III) ions often reduced from cyanide electrolytes at acidic, neutral or alkaline pH by means of electron receiving cathodically to elemental gold. By varying the temperature, voltage or current and electrolysis time, layer thicknesses can be from 0.1 microns to 200 microns produce. Applications of this method lie in electrical engineering for gilding of electrical contacts or in the surface treatment of the electrical solder pads on circuit boards. In these cases, the gold plating is used to prevent corrosion of the contact surfaces.

In the field of electronics, four different types of gold are applied:

• Soft gold plating in the semiconductor technology. It is used for gold plating of the pads on the semiconductor chip. In this so-called pads and usually consisting of gold bonding wires to be contacted, which constitute the electrical connection between the semiconductor chip and the external connection pins are located on the chip package. The Knoop hardness of the soft gold plating is in the range of 60-85.
• Hard gold plating of electrical contacts. This has a Knoop hardness of 120-300 and a purity of just over 99%. The remaining components are a small amount of nickel or cobalt. Chemical reasons this form of gold plating can not be used in the field of semiconductor technology for contacting semiconductor chips.
• Hard gold plating of electrical contacts on circuit boards as they are usual with platinum plugs. The gold plating is necessary because the plug contacts of the PCB connector a higher mechanical stress than other areas subject to a printed circuit board.
• Soft gilding of the lands on electrical circuit boards. This gold plating serves to protect the existing copper solder pads during storage from oxidation with the aim of being able to use in the soldering process less aggressive flux. Only the areas of the circuit board are gold plated which contact electronic components in further manufacturing process, the remaining part of the circuit board is covered by a passive solder resist. Through the assembly of printed circuit board with electrical components and the subsequent soldering the gold layer goes into solution with the solder and loses its meaning.

When gilding only certain base materials can be plated. For example, the copper used in electrical engineering because of its good electrical conductivity can not gild permanently directly, since copper has a tendency to diffuse through the thin gold layer to attach to the gold surface and oxidize there. Remedy multilayer electroplating process in which first the copper carrier, a thin layer of nickel is electroplated and only the nickel layer is then plated with gold. The additional layer of nickel in the outer region, however, it comes to poorer high-frequency characteristics of the line, according to the skin effect.

The next frequent in electrical copper conductor material aluminum tends contact with gold, such as gold-plated switch contacts, the formation of undesirable intermetallic compound AuAl2, which is also known as purple purple plague because of their typical color.

Ceramic Aufbrennvergoldung

By specially prepared solutions of gold salts and adhesion promoters such as rhodium ( III ) oxides can be a metallic gold contract on glass and ceramics reach. Depending on the parameters, the metal appears in matt or gloss after firing. The method is used in the dental preparation, but also for gilding of ceramic, porcelain ( gold rim ) and glasses.

Roll gilding

The gold plating ( Gold Filled ) based on mechanical association of foreign metal and gold plate by strong pressure. The method is used for semi-finished products, resulting in cheaper gold jewelry is manufactured, applied. The rolled gold plating is permanent and very durable. A disadvantage of the roll gilding is that the items are not covered on all sides. Walzgolddoublé certain strength is also a quality indicator.

Vacuum evaporation

The metal is deposited by a PVD or CVD method as a gold vapor on the workpiece to be coated. Plastics such as CDs and other delicate materials can thereby be coated with gold.

Anreibevergoldung

This group of methods is to be regarded rather as a historically and has been largely supplanted by the electroplating process. Specifically, all methods that use mercury or amalgam, are very harmful and pose a major environmental impact dar.

Red gold is produced by dipping the hot piece in Glühwachs, green with silver- gold amalgam. For matting of the gilded objects by heating it with a molten mixture of saltpeter, alum and salt, developed the chlorine and dissolves gold. To avoid disadvantages of fire gilding, by coating the objects also electroformed with mercury, then plentifully with gold and again with mercury and smokes from. Copper consumes more gold than red brass, and silver gilding appears little lively. Gilded silver is called vermeil.

Iron and steel are amalgamated by boiling with mercury, zinc, iron (II ) sulfate, water and hydrochloric acid, and then treated them like Tombak. In the cold gilding on copper, brass, nickel silver and silver gold scale ( with gold ( III ) chloride -soaked and burnt canvas) is rubbed by the finger or in salt water dipped slightly charred cork to the bare metal and polished with bloodstone. It is much less durable than the gilding on silver, but more beautiful than this and is therefore often set to very weak fire gilding. In wet gilt copper, brass, red brass, nickel silver, copper plated steel, tinplate be dipped into dilute gold chloride solution or in a boiling mixture of those with potassium carbonate, then rinsed, dried and polished. However, it only receives light gilding.

For green gold are added to the gold (III ) chloride silver nitrate. For wet gilding of silver (also: Greek gilt) dipping it into a solution of mercury (II ) chloride and gold in nitric acid. Iron and steel, copper-plated one or first immersed for etching with nitric acid in ether gold (III ) chloride solution. This is to be amplified by repeated immersion gold plating adhere more tightly to nitric acid corroded matt steel. Permanently Ethervergoldung is never. It therefore coppers iron and steel, and then uses the hot solution with potassium carbonate. It also connects the steel by means of a wire with zinc and dips it with this in a solution of gold cyanide in potassium cyanide ( cyanide ) and potassium thiocyanate.

Gilding

This very old method has already been used by the Egyptians. It has very little in common with the hot-dip galvanizing, despite the name analogy. The gilding is a piece of metal, usually steel, Colorful metals or silver, covered with gold amalgam and then heated. The mercury evaporates from the amalgam and the pure gold remains. Subsequently, the area with Bloodstone, also be polished hematite. Strict requirements for the emission and Employment Protection Act must be met for the application of this method.

Other methods

Gilding porcelain to use of gold ( III) chloride by means of oxalic acid or iron ( II) sulfate and precipitated with basic bismuth ( III) nitrate as a flux mixed gold; it needs to be polished after firing.

The gloss gilding (also gloss oil gilding and Meissen gilt), however, provides directly a shiny surface. It is obtained by burning in a solution of sulfuric gold or fulminating gold in sulfur balm, but is much less durable; it is already, if one feeds them a few times against the hair as taken away from a fine file.

As French Gilding refers to the treatment of brass with Lüstersud.