Not every unusual-looking coin has a minting error. Scratches, polishing, corrosion, dents and changes after a coin left the Mint can look dramatic but are usually damage rather than a collectible error.
Begin with the basics
Compare the coin with the correct date, denomination and design. Check both sides, the edge, diameter and weight against reliable published specifications. A difference in weight or colour can have several explanations and does not prove an error or authenticity.
What a minting error might look like
A genuine production error may involve an unusual strike, alignment, planchet or design feature. It should be consistent, clearly visible and supported by comparison with known examples. Photographs alone cannot authenticate an error or establish a premium.
Common damage after minting
- Scratches, dents and edge knocks
- Polishing or chemical cleaning
- Heat, corrosion or environmental discolouration
- Damage caused by machines or other coins
What to do next
Do not clean the coin or alter it further. Record the details, compare official specifications and seek an independent specialist opinion if it appears unusual. Read the safe UK coin research method before comparing prices.