White spotting on silver coins - Dr Matthew Williams, The Royal Mint
Matthew Williams
Director of Engineering and Quality, The Royal Mint
White spotting on silver coins
Tuesday the 25th of November 2025 at 18:00
Room N1.32 School of Engineering, Cardiff University, 5 The Parade, Cardiff, CF24 3AA
**Note this is not our usual room! N1.32 is on the first floor of the North Building, opposite the Trevithick Building. Please note that it is necessary to pay for parking, instructions are displayed on signs in the car park.
The lecture will also be streamed live, to register please use this link:
events.teams.microsoft.com/event/926d51c1-f30f-4235-9ebd-adba591ec9c6@bdb74b30-9568-4856-bdbf-06759778fcbc
Abstract
The occurrence of white spotting on silver coins remains a significant quality concern for the minting industry. These surface defects, often associated with sodium chloride and other atmospheric contaminants, compromise both the visual appeal and long-term stability of silver products. In this work, we have developed and implemented an invisible barrier coating to mitigate the interaction between silver surfaces and environmental species responsible for white spot formation. The coating provides a protective, non-intrusive layer that preserves the natural appearance of silver while preventing chloride adsorption and subsequent corrosion pathways. This advancement represents a step change in surface engineering for coinage, offering improved product reliability and customer satisfaction. By embedding this protective technology within the minting process, we aim to enhance product performance, reinforce brand reputation, and secure greater market competitiveness.
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