Convention & Other Legal Marks

The Convention on the Control and Marking of Articles of Precious Metals (known as the Hallmarking Convention) is an international treaty between Contracting States, which aims to eliminate trade barriers in the cross-border trade of precious metal articles.

Signed in Vienna on 15 November 1972, the Convention came into force in 1975. Its text was mainly drafted and negotiated in Geneva and London, and Goldsmiths’ Hall is widely considered the Convention’s ‘birth place’.

The UK has been a signatory to the International Convention on Hallmarks since its inception 1972.


Example Common Control Marks, for l-r silver, palladium, gold, platinum

Example of silver convention mark

Example of 18ct gold convention mark

This means that the Goldsmiths’ Company Assay Office can strike the Convention Hallmark which is recognised by all member countries in the International Convention. Conversely, articles bearing the Convention Hallmark (marked in Member states) are legally recognised in the UK and do not have to be re-hallmarked here. So, this mark eases and ensures safeguards for the cross border trade of jewellery. 

Finenesses recognised under the Convention are:

  • Gold - 375, 585, 750, 916, 999.
  • Silver - 800, 925, 999.
  • Platinum - 850, 900, 950, 999.
  • Palladium 500, 950 and 999

A Convention Hallmark comprises four marks:

  • Sponsor's mark
  • Common Control mark
  • Millesimal fineness mark
  • Assay Office mark 

2015 marked the Convention's 40th Anniversary - read more here

Other legally recognised marks in the UK

National hallmarks from certain European countries are recognised in the UK if they are deemed equivalent and are intelligible.  The situation regarding these is unclear at the moment due to the Brexit decision.

The Member Countries of the Convention are:
Cyprus The Netherlands
Czech Republic Norway
Croatia Poland
Denmark* Portugal
Finland Slovak Republic
Hungary Slovenia
Ireland Sweden
Israel Switzerland
Latvia Austria
Lithuania United Kingdom

*including Greenland

Croatia, Italy, Serbia, Sri Lanka  and Ukraine are in process of acceding to the Convention.

The IAAO, an unincorporated organisation, now comprises more than 60 members from over 40 countries.  Not all members of the IAAO are members of the Convention.

  • International Convention mark; Sponsor’s mark, Common Control Mark, millesimal fineness mark, and assay office town mark.

    International Convention mark; Sponsor’s mark, Common Control Mark, millesimal fineness mark, and assay office town mark.

  • Common Control Mark

    Common Control Mark