Do commemorative coins tarnish over time?
With time, all coins show signs of ageing. Various terms are used to describe this process such as tarnishing, discolouring and toning. It is a natural process, although the speed at which it progresses depends largely on the environment in which the coins are kept. In most instances, it is usually a very slow process.
The tarnish on a coin is made up of the product of the corrosive element in the atmosphere and the metal from the coin surface. Here at The Koin Club we continually improve the production process for proof coins and how to store coins and therefore, our more recent products are less likely to tarnish.
However that is not to say that the newer products will not tarnish; as indicated, this is a natural process.