Gold, which is probably the earliest noble metal known to man, is in its purest form too soft to be used for jewellery. Today though, this form, "24-karat" gold, is available in Thailand, Indonesia, Singapore, and Hong-Kong, Gulf countries and most recently in India. It is because of this soft nature that gold has to be alloyed with other metals to give it a proper hardness, malleability and ductility before it is used to make jewellery. 'Karat', which is the unit that defines the purity of gold, is a term that is as old as the history of gold. Karat is a scale from 0 to 24, 24 carats being 100% pure gold. In this scale a simple mathematical proportion is used, 14 carats for example says that 14 out of 24 part is gold while the other 10 parts are the metal that the gold sample under examination has been alloyed with.
Gold is also mixed or alloyed with one or more other metals to give it certain color and characterstics.

Making Gold Alloys

(Note: The standards used here are British or European in which the requirement is that the result be 1/2 karat higher than stamped.)

In Europe, the purity is measured in fineness and 24 carat is 999 fine.

HALLMARKING

A Hallmark is an official mark or a special punch bearing a figure or numbers, imparted by a single blow onto an object made of precious metal that is offered for sale, in order to show that its quality confirms with legal standards. The Hallmark is applied to such objects as a means of safeguarding the purchaser against fraud. Hallmarks are also used on articles made of non-precious metals for purposes of maker's identification, to indicate place and date of manufacture, and to apply other identifying marks.

Official marks to designate and guarantee the purity of precious metal ingots were in use as far back as 2000 B.C. in Egypt when the method was developed of removing impurities (in the form of other metals including silver) from gold, leaving it at least 95% pure.

Hallmarking is an official governmental function in modern times which began in 13th century in France with the use of townmarks, such as at Montpellier. By royal decree in England in 1300 A.D., all articles made of precious metals had to be brought to Goldsmith's Hall in London, the guild hall of the goldsmiths who were entrusted with the testing of all such articles for purity and compliance with set standards. If the article met those standards, it could be stamped officially with the mark of the Goldsmith's Hall, now generally referred to as the hallmark, and it could be sold. Such rigid control served to guarantee the purchaser that any object so marked was without question made of the quality of metal the hallmark declared it to be.