The chemistry or alchemy of coinage was probably invented in the Mediterranean and from there transmitted to other ancient civilizations. The minting of British coins appears to have begun in the 1st century AD but ceased with the Roman occupation, although the Romans minted coins in London in the 3rd century. After the Roman withdrawal, minting again ceased until the 7th century but by the 9th century London had become the dominant centre for minting, a position it maintained following the Norman Conquest.

Minting at the Tower of London may have begun as early as 1248 and was well established by 1279. Over subsequent years the organization of the mint became more structured, incorporating procedures to test and safeguard the purity of the coinage. By the 14th century minting activities were largely concentrated at the Tower, although provincial mints remained in operation until the reign of Henry VIII. The quality of its coinage was important both to a country’s internal social stability and to its reputation abroad. Consequentially the site of the mint’s operations at the Tower was recognized as a prestigious place and the rights and privileges of its senior officers were protected by royal privilege.

In the late 1970s workmen at the Tower unearthed strips of metal and other material relating to the minting process. Although records are scarce, subsequent excavations off Mint Street have produced large quantities of finds and revealed two main workshops together with a number of small buildings located between the inner and outer curtain walls on the east side of the Tower. Each room would have been devoted to a specific stage of the complex minting process. Features include a hearth with fired clay floor; an ash pit; a pair of furnaces; benches; crucibles and vitrified bricks from the furnaces. There is evidence that crucibles were being manufactured on site, whilst traces of gold and other metal within fragments of the crucibles, together with strips of impure copper, suggest that both base and precious metals were being refined and melted in the workshops. The finds reflect processes typical of a 16th century mint, although close dating of the activities has not been possible.

Henry VIII is known to have instituted a series of debasements of the coinage, replacing up to 80% of gold and silver with base metal such as copper, in order to reduce debts incurred as a result of his foreign wars and extravagant building programmes. Edward VI continued to issue debased pennies but increased the purity of higher value coins.

Jennifer Hunt