Jewellery Catalogue co.uk

Gold Assay

To assay a metal is to subject it ( such as silver or gold) to chemical analysis, to determine the amount of alloy.
Cupellation or fire assayThe most accurate and widely used method, with an accuracy of 2-3 parts per ten thousand (0.02%), is the Fire Assay (Cupellation) method. This involves taking a small scraping from the article, typically about 250 milligrammes, weighing it accurately, wrapping it in lead foil with some added silver, cupelling it in in a furnace at about 1100°C to remove all base metals and then placing the resulting gold-silver alloy button in nitric acid to dissolve out the silver (known as 'parting') and re-weighing the resulting pure gold. This is the standard reference technique used by the national Assay laboratories worldwide for Hallmarking and is covered in the International Standard, ISO 11426:1993.

A simplification of this technique involves omitting the initial cupellation stage and just melting the sample with added silver and/or copper, rolling to a thin sheet and then dissolving out the silver and base metals with nitric acid. This is satisfactory only when there are no other impurities present, is less accurate, but generally sufficient for most small workshops.

Hallmarks

Carat Fineness, % Gold content, % Comments
24 999 99.9 Three nines
24 990 99.0 Two nines, Minimum allowed
22 916 91.6 Indian subcontinent
21 875 87.5 Arabic countries
(19.2) 800 80.0 Standard in Portugal
18 750 75.0 Standard caratage
14.8 620 62.0 Dental Gold Minimum
14 585 58.5 583/58.3% in USA
10 417 41.7 Minimum in USA
9 375 37.5 U.K. standard
8 333 33.3 Minimum Germany

Hallmarking is the application of a quality control mark to an article of precious metal. It is also called an assay or standard mark. They are usually applied after accurate independent testing by one of four UK assay Offices which are legally empowered to test precious metals and apply a hallmark to them. These offices are Birmingham, Edinburgh, London and Sheffield.

Date Letters
A hallmark indicates that an article has been independently tested at an Assay Office and guarantees that it conforms to the legal standards of precious metal content, known as the fineness.
A hallmark indicates at least three facts:

Who made the article (makers mark)- the initials of the maker What the metal is, and its purity - the fineness mark Where it was tested (Assayed) and marked - the Assay Office mark

The Leopard's Head is the mark of the London Assay Office and has been in continuous use since 1300, when the Wardens of the Company were given responsibility for marking gold and silver wares, which passed assay, with the King's mark of the Leopard's Head. A handy guide to hallmarks from the different Assay Offices can be purchased quite inexpensively from your local bookstore.


Fineness
The fineness of the precious metal content of jewellery and silverware is expressed in parts per thousand. Sterling silver is indicated by 925, which means it is 92.5% silver or 925 parts of silver in every 1000 of the silver alloy. The current legislation is the Hallmarking Act 1973. Following amendments to the Act in 1998 and January 1999, the sponsor's mark, fineness mark and Assay Office mark remain compulsory. But the Date Letter indicating the year of hallmarking, which had been in use from 1478, is now a voluntary mark, as are the traditional fineness symbols, the Lion Passant for 925 Silver, Britannia for 958 Silver and the Orb for 950 platinum. Platinum was only recognised as a hallmarkable precious metal since 1976.

The standards of fineness are:

Metal: Compulsory Mark
9ct gold 375
14ct gold 585
18ct gold 750
22ct gold 916
99% pure gold 990
99.9% pure gold 999
800 grade silver 800
sterling silver 925
Britannia Silver 958
99.9% pure silver 999
85% Platinum 850
90% Platinum 900
95% (UK standard) Platinum 950
99.9% pure Platinum 999

An article cannot be legally described as being of gold, silver or platinum unless it is hallmarked, or the article weighs less than 0.5 grams in platinum, 1 gram in gold or 7.78 grams in silver.

The history of gold and silver quality standards goes back to the early uses of these metals as money. Legal regulations governing the marking of jewellery began here in the UK in 1239 and in one form or another have existed throughout the civilised world since.
Penalties for violation of these laws have varied. In 1397 a report was made on the false counterfeit stamps of two goldsmiths who were sentenced to be placed in the pillory at Westminster with their ears nailed to it and with a ticket over their heads upon which their offences were written. They each later had one ear cut off, were imprisoned and fined 10 marks.

 

THE HALLMARK NOW COMPRISES A MINIMUM OF THREE SYMBOLS:

SPONSOR
The registered mark of the maker or the sponsor of the piece

GOLD SILVER PLATINUM
NUMBER
The millesimal number indicating the precious metal content. The shape of the shield identifies the metal as gold, silver or platinum
ASSAY OFFICE
The mark of the Assay Office where the piece was tested
THERE MAY BE ADDITIONAL MARKS SUCH AS DATE LETTER:

Further information, including details of other Hallmarks and Standards, can be obtained from any of the Assay Offices of Great Britain (London, Birmingham, Sheffield, Edinburgh) or
The British Hallmarking Council,
PO Box 18133
London
EC2V 8JY

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