Coin collectors have been left angered after some commemorative silver coins that cost £55 turned brown, rendering them completely 'worthless'.
The coins that have been discoloured were 50p pieces celebrating the lives of Stephen Hawking and Sir Isaac Newton, as well as some that commemorated the UK leaving the European Union.
The affected coins were minted mostly in 2019 and 2020, but some of the browned currency dates back to 2017.
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As well as the commemorative 50 pieces, the problem has also been observed in a silver proof 20p coin as well.
The process by which the colour of a silver coin changes is called toning or tarnishing and is caused by a chemical reaction between the metal surface of the coin and oxygen occurring naturally in the air.
It's usually seen only in older coins, and often relates to the environment that the coin has been kept in.
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However, it does mean that the value of the coins takes a hit, which is annoying if you've paid a fair whack for the coin, or are someone who collects them.
People who do collect coins - or numismatists, if you like - usually do so in the hope that they'll gain value over the years.
This counts double for commemorative coins, as they're usually in mint condition and not in general circulation.
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Silver proof coins cost a bit more to buy from the Royal Mint because they do become more valuable over time.
In this instance, the affected coins have all been kept in the Royal Mint's special packaging, leading some to believe that it's the foam they're stored in that is causing the discolouring.
Colin Bellany, the man behind Coin Hunter, told The Sun: "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.
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"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."
A spokesperson from the Royal Mint said: "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.
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"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."
Featured Image Credit: Coin Hunter/Colin Bellany