A hallmark is an official mark or series of marks struck on items made of precious metals—
platinum, gold, silver
In a more general sense, the term hallmark can also be used to refer to any distinguishing characteristic or trait.
Historically, hallmarks were applied by a trusted party:
the 'guardians of the craft' or nowadays by an assay office.
Hallmarks are a guarantee of certain purity or fineness of the metal as determined by formal metal (assay) testing.
In the UK, the hallmark is made up of several elements including: a mark denoting the type of metal, the maker/sponsor's mark and the year of the marking. In England, the year of marking commences on May 19, the Feast Day of Saint Dunstan, patron saint of gold- and silversmiths.
How Pure Is Your Gold Jewelry?
18K, 14K, or 10K, with the K standing for karat, the system used to describe the percentage of pure gold an item contains. The higher the karat number, the higher the percentage of gold in your gold jewelry.
24K gold is pure gold.
18K gold contains 18 parts gold and 6 parts of one or more additional metals, making it 75% gold.
14K gold contains 14 parts gold and 10 parts of one or more additional metals, making it 58.3% gold.
12K gold contains 12 parts gold and 12 parts of one or more additional metals, making it 50% gold.
10K gold contains 10 parts gold and 14 parts of one or more additional metals, making it 41.7% gold. 10K gold is the minimum karat that can be called "gold" in the United States.
European Markings
European gold jewelry is marked with numbers that indicate their percentage of gold, such as:
18K gold is marked 750 to indicate 75% gold
14K gold is marked 585 for 58.5%
10K gold is marked 417 for 41.7%
In the UK 9k and 18k is the most common
In the USA 10k
you will find 9k, 10k, 14k, 15k, 18k, 20k, and 21k
In the modern world, in an attempt at standardizing the legislation on the inspection of precious metals and to facilitate international trade, in 1973 a core group of European nations signed the Vienna Convention on the Control of the Fineness and the Hallmarking of Precious Metal Objects.
Those articles, which are assayed and found to be in conformity by the qualifying office of a signatory country, receive a mark, known as the Common Control Mark (CCM), attesting to the material's fineness.
The multi-tiered motif of the CCM is the balance scales, superimposed, for gold,
on two intersecting circles; for platinum,
a diamond shape and for silver a mark in the shape of the Latin letter "M".
This mark is recognized in all the other contracting states, including: Austria, Cyprus, the Czech Republic, Denmark, Finland, Great Britain, Hungary, Ireland, Israel, Latvia, Lithuania, the Netherlands, Norway, Poland, Portugal, Sweden, Switzerland
As it now stands, the compulsory part of the UK hallmark consists of the sponsor or maker's mark, the assay office mark, and the standard of fineness (in this case silver, 925 parts in 1000).