The Trial of the Pyx
The history of the Trial of the Pyx dates back to the twelfth century, making it one of the longest established judicial procedures in the country. The purpose of the annual trial is to check that UK coins produced at the Royal Mint are within the statutory limits for metallic composition, weight and size. The name Pyx refers to the chests in which the coins are transported, and derives from the Pyx chamber in Westminster Abbey where historically the chests were kept, along with other important items of state and church.
By the thirteenth century the Trial of the Pyx had begun to take the form that we know today. Early trials were held first in Westminster Hall and later in the Exchequer at Westminster. But in 1870, as laid down in the Coinage Act of that year, Goldsmiths' Hall became the established venue for the Trial. This made good sense with the The Goldsmiths' Company Assay Office collocated in the Hall, as it is today. It is the Assay Office, whose familiar hallmark is synonymous with quality, which has the task of testing the metallic composition of the coins.
The benchmark against which coins are tested is called a Trial Plate. These metal plates of gold, silver, platinum and cupro-nickel, which used to be under the personal charge of the monarch in the Exchequer, are now the responsibility of the National Measurement Office, along with the weights against which the coins are measured.
In February each year, officials from the Royal Mint bring chests (pyx) to Goldsmiths' Hall, containing coins put aside in the course of manufacture during the previous year. These coins, normally more than 50,000 in total, represent one coin from every batch of each denomination minted.
The trial jury, comprising members of the Goldsmiths' Company, is summoned to the Hall by the senior judge in the Courts of Justice, known as the Queen's Remembrancer, and is a formal court of law. During the opening proceedings the coins are counted and weighed, and a selection put aside for testing by the Assay Office.
A short video clip of the 2013 Trial of the Pyx below:
The Delivery of the Verdict, presided over once more by the Queen's Remembrancer, takes place some two months later, once the Assay Office has verified the coins. It is attended by the Chancellor of the Exchequer (who is the Master of the Mint) or his representative.