Prime Warden 2018-19, Michael Prideaux, holds a gold commemorative WWI coin. The Trial of the Pyx at Goldsmiths Hall. One of the longest established judicial procedures in the world, dating back to the thirteenth century, this ancient ceremony has a direct relevance to every user of UK coinage today. The Trial of the Pyx fulfils a legal requirement imposed by an act of Parliament (Coinage Act 1971) to conduct an examination by jury to ascertain that the coins of the realm, produced by the Royal Mint, are of the correct weight, size and composition. London, UK.