COIN collectors have been left fuming after their £55 commemorative coins turned brown making them “worthless”.
The discolouration has occurred on a range of different silver proof 50p coins, including designs celebrating Stephen Hawking and Sir Isaac Newton, and ones marking Brexit.
The majority of affect coins were minted in 2019 and 2020, although some date back to 2017.
While most of the browning coins are 50ps, the problem has also occurred in a 20p coin too.
Discolouration on coins is called “toning” or “tarnishing” and is a natural process caused by a chemical reaction between the metal surface and the oxygen in the air.
The speed at which it happens depends on the environment the coins are kept in and usually occurs in older coins – but it can significantly devalue its worth.
Collectors tend to invest in commemorative coins because they’re likely to go up in value in the future.
Generally, the resale value is higher than a circulated coin because of it’s mint condition, which is why they’re often kept in air-tight cases to protect them.
Silver proof coins are the highest quality commemorative coins produced by the Royal Mint, making them even more valuable than brilliantly uncirculated ones.
Typically, they cost £55 when bought directly from the coin maker but can soar in value as time goes on.
For example, a 2016 silver proof Peter Rabbit 50p coin recently sold on eBay for £595 – that’s more than nine times what it was bought for.
It’s £495 more than what a circulated version of the coin fetched on the auction site a few months ago.
Scores of collectors have contacted Coin Hunter after experiencing the same issue.
Affected coins are all being stored in the packaging issued by the Royal Mint, leading Colin Bellany – who’s behind Coin Hunter – to believe that there may be a chemical in the foam holder that is causing them to change colour.
He said that a large number of customers are upset that the coins, which are often bought as an investment, have devalued in this way.
Colin added: “As these coins have been stored in many different households, often alongside other coins that are not tarnishing – The Royal Mint will want to carry out tests on these coins and the packaging to try and determine the cause.
“If the cause relates to any part of the manufacturing process of the coin or packaging, I would hope that The Royal Mint will offer a replacement or refund to all affected customers.”
The Royal Mint makes over 200,000 silver proof coins every year.
Over the years, it has “continually improved the production process for proof coins” and as a result the more recent products are less likely to tarnish.
It told The Sun new coins changing colour like this is incredibly rare and that says there is no indication that it is a wider issue.
A spokesperson added: “All of our silver proof coins are sold in airtight containers and secure display cases to help protect the metal, and enable collectors to enjoy the design.
“Tarnishing is known to be a natural, long term side effect of silver and we recommend that customers keep coins in their protective casing.
“Storing silver in a humid or damp environment contributes to premature tarnishing, and could be a factor in this case.
“We are in contact with the customer to understand their specific circumstances – but there is no indication of a wider issue.”
Circulated coins can also be valuable – here’s our guide to the most valuable and rarest 50ps.
One 50p designed to commemorate 250 years since Samuel Johnson published his dictionary recently sold for £2,800.
Plus, a rare Battle of Hastings 50p coin sold for £63,000 last month, while an Olympic swimmer error coin fetched £10,100 online.