It makes sense that a Roman sestertius and its mint-twin from the same die could end up having very different values after centuries, and it has nothing to do with the value that the two coins had originally. As one was buried and the other was not, in the end it is the two different biographies that the two coins have had that will be the bulk of the value of the coins when they reach the auction block.
The strange science of patina
The ‘patina’ on a coin (its skin) is something to be cherished. On copper and bronze coins, the green Verdigris will often appear to be damage, but in fact it is the reverse. The stable copper carbonate patina forms slowly over the centuries to seal the surface of the coin and reveal the many fine details that otherwise would be lost. But, oh so easily, this precious skin can be scrubbed away in an instant, usually by someone with the best of intentions, but who has no idea of the damage being done. In a matter of seconds, ten at the most, the coin will have been stripped of its patina and be left with a host of minute scratches that will be revealed instantly by even poor-quality lighting. The coin will have been ruined, its grade stone dead. All collectors can tell when a coin has been ‘cleaned’, it has an unnatural shine, far too bright and even, rather like one who has been on suntan parades.
Why coins get buried
A great many coins were buried in the earth for the very same reasons that people today take large amounts of cash with them on a journey into the unknown. Many of these coin hoards were buried by their owners with every intention of returning to retrieve them. It never worked out that way. Many are still buried today. Some have been discovered; others remain lost for all time.
For those who are interested in the value of coins, before they can be valued, they have to be identified. This is known as attribution, and it can take days for a numismatist to cross reference the worn legends on a coin with information from other similar coins to confirm the identity of the emperor, the mint and the issue. There is a great sense of satisfaction when the attribution is confirmed especially for those who are not familiar with coins.
Hosker Haynes a coin auctioneer here in the UK with focus on coins that have been through all the events in their life, prior to coming to auction.
The coin on the block is already the most eventful it is ever going to be. What happens at the auction is almost incidental.
