Gold plating and Gilding, history and anagrams

Gold is a metallic element with a characteristic yellow ( or golden ) colour, but can also be black or ruby when finely divided. These colours are a result of gold's plasmon frequency lying in the visible range, which causes red and yellow light to be reflected, and blue to be absorbed. Only silver colloids exhibit the same interactions with light, albeit at shorter frequency, making silver colloids yellow.

Gold plating is a method of depositing a gold layer on the surface of other metal, most often copper or silver, by chemical or electrochemical means. Mechanical or chemical affixing of thin gold foils on the surface of objects is instead known as gilding.

Gold plating is used in electronics, to provide a corrosion resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards. With direct gold on copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of surface and formation of an oxide / sulfide layer.

Jewelry
Gold plating of silver is often used in jewelry. However, like copper, silver atoms undergo diffusion through the golden layer, causing slow gradual fading of colour and causing surface tarnishing . This process may take months to years, depending on the thickness of the gold layer. A barrier metal layer is used to counter the effect; often copper, while migrating through gold as well, is much slower in this process, and it is usually further plated with nickel. Therefore a gold - plated silver is usually a sandwich of silver substrate with layers of copper, nickel, and gold deposited on top of it.

Plating is the general name of many surface- cover techniques in which a metal is coated onto a solid surface. Plating is indispensable for the manufacture of computers, mobile phones, and electronic devices as well as for surface treatment techniques. Moreover, it is a key technology for the development of new machines. It is also used for decoration, typically to provide a silver or gold exterior. Thi n- film deposition techniques have accomplished plating on scales as small as the width of an atom, so it is appropriate to call some plating applications nanotechnology.

There are several plating methods. For example, in one method, a solid surface is covered with a metal sheet and then plated by heating. Other plating techniques include vapor deposition under vacuum, sputtering, and methods using vacuum conditions or gas. Recently, however, only plating techniques using a liquid tend to be called "plating". Metallizing refers to the process of coating metal on non-metallic objects.

A problem can occur since Gold plating can lead to formation of gold whiskers.
Soldering to gold-plated parts can be tricky. Gold dissolves in solder; an alloy of solder which contains more than 5% of gold can become brittle and the joint surface is dull-looking. If the gold layer does not completely dissolve in the solder, it may be pulled off the underlying surface later as the tin and gold atoms cross-migrate and undergo Kirkendall voiding, leading into a mechanical failure of the joint; a similar process on the gold - aluminum interface is known as purple plague. Thin layers of gold dissolve in the solder, exposing the underlying metal to the solder.

A 2-3 µm thick layer of gold is easily dissolved within a second during typical wave soldering conditions.
Types of gold plating
There are several types of gold plating used in electronics industry

Chemistry of Gold Plating
There are five recognized classes of gold plating chemistries:

Alkaline gold cyanide, for gold and gold alloy plating.
Neutral gold cyanide, for high purity plating.
Acid gold plating for bright hard gold and gold alloy plating.
Non-cyanide, generally sulfite based for gold and gold alloy plating.

Electroplating
Electroplating is the process by which a metal in its ionic form is supplied with electrons to form a non - ionic coating on a desired substrate. The most common system involves a chemical solution that contains the ionic form of metal, an anode which may consist a metal being plated or an insoluble anode, and finally, a cathode where electrons are supplied to produce a film of non-ionic metal.

Electroless plating
Electroless plating, also known as chemical or auto-catalytic plating, is a non-galvanic type of plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite, and oxidized thus producing a negative charge on the surface of the part. The most common electroless plating method is electroless nickel plating. Electroless nickel plating

Other types of plating

Silver plating
Rhodium plating
Chrome plating
Zinc coatings
tin plating

Gilding is the art of spreading gold, with either mechanical or chemical means, over the surface for the purpose of ornament.

The art of gilding was known to the ancients. According to Herodotus, the Egyptians often were known to gild wood and metals and gilding by means of gold plates is frequently mentioned in the Old Testament. Pliny the Elder stated the first gilding seen at Rome was after the destruction of Carthage, under the censorship of Lucius Mummius, when Romans began gilding ceilings of their temples and palaces, the Capitol being the first place on which this process became used.

Gilding has occupied an important place in the ornamental arts of Oriental countries; and the native processes pursued in India at the present day may be taken as typical of the arts as practised from the earliest periods.

For the gilding of copper, employed in the decoration of temple domes and other large works, the following is an outline of the processes employed. The metal surface is thoroughly scraped, cleaned and polished, and next heated in a fire sufficiently to remove any traces of grease or other impurity which may remain from the operation of polishing. It is then dipped in an acid solution prepared from dried, unripe apricots, and rubbed with pumice or brick powder. Next the surface is rubbed over with mercury, which forms a superficial amalgam with the copper, after which it is left some hours in clean water, again washed with the acid solution, and dried. It is now ready for receiving the gold, which is laid on in leaf, and, on adhering, assumes a grey appearance from combining with the mercury, but on the application of heat the latter metal volatilizes, leaving the gold a dull greyish hue. The colour is brought up by means of rubbing with agate burnishers. The weight of mercury used in this process is double that of the gold laid on.

For the gilding of iron or steel, the surface is scratched over with chequered lines, then washed in a hot solution of apricots, dried and heated just short of red-heat. The gold leaf is then laid on, and rubbed in with agate burnishers, when it adheres by catching into the prepared scratched surface.

For the traditional gilding of carved wood, a thin layer of white gesso is applied to the carving, which may be touched up for crispness by recarving details. A reddish or ochre water-based bole is applied, the colour of which will affect the colour of the finished gilding. Gold leaf is applied and burnished with a dog's tooth.

Mercury gilding was the technique employed for European gilt bronze.

Modern gilding is applied to numerous and diverse surfaces by various distinct processes, so the art is prosecuted in many ways, and is part of widely different ornamental and useful arts. It forms an important and essential part of framemaking. It is largely employed in connection with cabinet work, decorative painting and house ornamentation and also bulks largely in bookbinding and ornamental leather work. Further, gilding is much employed for coating baser metals, as in button-making, in the gilt toy trade, in electro-gilt reproductions and in electroplating; and it is also a characteristic feature in the decoration of pottery, porcelain, and glass. The various processes fall under one of two headings mechanical gilding and chemical gilding.

Mechanical gilding embraces all the operations by which goldleaf is prepared, and the several processes by which it is mechanically attached to the surfaces it is intended to cover.

Chemical gilding embraces those processes in which the gold used is at some stage in a state of chemical combination. These include Cold Gilding: Wet gilding Fire-gilding or Wash-gilding.
Gilding of Pottery and Porcelain: The quantity of gold consumed for these purposes is very large. The gold tised is dissolved in aquaregia, and the acid is driven off by heat, or the gold may be precipitated by means of sulphate of iron.

Foreign names

Gold

Germany it is known as Gold

In Spain, and Italy it is known as Oro

In Finland it is known as Kulta

In france it is called Or

In Poland it is called Zloto

Anagrams

Gold plating = Pig doll gnat

'Gold plate' = 'top Lag led

birthplace of British PMs

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