Metallurgical assay and the U.S. Mint continue to produce precious metal bullion coins for collectors and investors. The precious metal purity and content of these coins is guaranteed by the respective mint or government, and, therefore, the assay of the raw materials and finished coins is an important quality control. In the UK, the Trial of the Pyx is a ceremonial procedure for ensuring that newly minted coins conform to required standards. Metallurgical assay A metallurgical assay is a compositional analysis of an ore, metal, or alloy. Some assay methods are suitable for raw materials; others are more appropriate for finished goods.
Coins of the pound sterling coins was reduced from 92.5% to 50%, with some of the remainder consisting of manganese, which caused the coins to tarnish to a very dark colour after they had been in circulation for long. Silver was eliminated altogether in 1947, except for Maundy coinage, which returned to the pre-1920 92.5% silver composition. The 1816 weight/value ratio and size system survived the debasement of silver in 1920, and the adoption of token coins of cupronickel in 1947. It even persisted after decimalisation for those coins which had equivalents and continued to be minted with their values in new pence. The UK