Derbyshire appears to have been a hotbed of coin counterfeiting in the past. Several counterfeit Roman denarii and 17th century half crowns and shillings have been discovered in the county and recorded with the PAS. Counterfeits were silver plated (e.g. DENO-DAAFF0), or made from base silver and disguised with a silver wash (e.g. PUBLIC-F070C6). They can be very high quality copies that would have looked genuine and are now only recognisable because of damage to the coins revealing the copper alloy core (e.g. DENO-9B79DE).
Later Roman coins were also copied, but not necessarily for malicious reasons. In AD 260, Britain, Gaul and Spain broke away from the rest of the Roman Empire, forming an independent Gallic Empire. The Gallic Emperors minted their own coins (based on radiates minted by the central Roman Empire) in Trier in large quantities, many of which are found in Britain. When the Gallic Empire was reabsorbed by the central Roman Empire in AD 274, coin minting in Trier ceased. The mints in Rome were not used to minting coins for Britain, so there was a shortage of radiates in Britain. The inhabitants of Britain had grown used to a monetary economy, so people began to make their own copies of radiates (known as barbarous radiates) out of old Roman sestertii and other pieces of scrap copper alloy. One of the most well known coin hoards from Derbyshire is the Amber Valley Hoard (DENO-A6AE06) which contains 3631 radiates, all but four of which are barbarous radiates. The barbarous radiates in the hoard are very crude; clearly not meant to fool anyone.
It was a common but illegal practice to clip the edges of silver coins in order to melt the silver down and use it for other things including counterfeiting coins. Until 1662, most coins were struck or hammered from irregularly shaped pieces of metal, so it was easy to get away with this crime.
Counterfeiting and clipping was a big problem for the authorities who made various attempts to prevent it. During the Roman Republic, some denarii were minted with serrated edges (e.g. DENO-C8C497), a feature thought to discourage counterfeiting. They were only short-lived so they were clearly not successful.
During the medieval period, the change from short cross to long cross coinage in 1247 was probably intended to prevent clipping. Coin clipping and counterfeiting was a crime punishable by death. In spite of these measures, coin clipping and counterfeiting continued and was particularly common during the English Civil War when counterfeiters thought that they were more likely to get away with it. Several hoards of clippings from that period have been discovered in Derbyshire. One of these was found in Alderwasley (DENO-060EAA). The video below is from a Blue Peter episode. Skip to 5:25 to see the finders talking about their discovery.
Derby also has a connection to coin counterfeiting. Noah Bullock set up a business on a boat on the River Derwent, where he clipped and counterfeited coins. He was arrested and only escaped the hangman’s noose because he knew the magistrate. The Noah’s Ark pub in Derby is named after him.
Many of the coins mentioned in the article are currently on display in Derbyshire Unearthed: Coins and Coin Hoards, an exhibition of Treasure and PAS finds at Derby Museum and Art Gallery.