The Trial of the Pyx is the procedure in the United Kingdom for ensuring that newly-minted coins conform to required standards. Trials have been held from the twelfth century to the present day, normally once per calendar year; the form of the ceremony has been essentially the same since 1282. They are trials in the full judicial sense, presided over by a judge with an expert jury of assayers. Trials are now held at the Hall of the Worshipful Company of Goldsmiths; formerly, they took place at the Palace of Westminster. Given modern production methods, it is unlikely that coins would not conform, but this has been a problem in the past — it was tempting for the Master of the Mint to steal precious metals.

The term "Pyx" refers to the boxwood chest (in Greek, πυξίς, pyxis) in which coins were placed for presentation to the jury. There is also a Pyx Chapel (or Pyx Chamber) in Westminster Abbey, which was once used for secure storage of the Pyx and related articles.

The judge having charge of the trial is the Queen's Remembrancer, the Senior Master of the Queen's Bench. It is his or her responsibility to ensure that the trial is held in accordance with law, and to deliver the final verdict to Her Majesty's Treasury. Where and when a trial is to take place is at the Treasury's discretion, though there must be a trial in any year during which the Royal Mint issues coins.

Coins to be tested are drawn from the regular production of the Royal Mint. The Deputy Master of the Mint must, throughout the year, randomly select several thousand sample coins and place them aside for the Trial. These must be in a certain fixed proportion to the number of coins produced. For example, for every 5000 bimetallic coins issued, one must be set aside, but for silver Maundy money the proportion is one in 150.

The jury is composed of at least six assayers from the Company of Goldsmiths. They have two months to test the provided coins, and decide whether they have been properly minted. Criteria are given for diameter, chemical composition, and weight, for each class of coinage.

Statutory basis for the Trial of the Pyx is given by the Coinage Act 1971, the latest in a long series of similarly-named Acts of Parliament. Specific procedures are established by Order-in-Council, the most recent being the Trial of the Pyx Order 1998. It is not required for a new Order to be issued for each Trial: this only happens when the rules change.

References

• Halsbury's Laws of England
• Trial of the Pyx Order 1998 (http://www.hmso.gov.uk/si/si1998/19981764.htm)
• Royal Mint description (http://www.royalmint.com/about/trialofpyx.asp)
• Company of Goldsmiths description (http://www.thegoldsmiths.co.uk/company/trial.htm)
• Pyx Chamber at Westminster Abbey (http://www.westminster-abbey.org/tour/pyx_chamber.htm)