My sister got me three Roman coins she bought in a lot off ebay. They are really tarnished and dirty, so much so that they are nearly unidentifyable. They came with "cleaning" instructions. I know cleaning is a no-no, but I really want to be able to identify these coins. I have no interest in selling these myself, but who knows what whomever I leave my collection to may want to do. Short story long, should I clean them so I can see through the tarnish and enjoy them, or leave them as is?
All ancient coins have been cleaned. The ones with a n inch of dirt still on them probably once had two inches. Modern US coins from 1793 and after are found that spent the intervening time in a bank vault or someone's drawer. Cleaning such coins is a big mistake. A few US coins are found with metal detectors and could be improved by proper cleaning but the social prohibition of this is so strong that many collectors consider cleaned coins in the same way they do holed coins. Ancients are a different matter. The vast majority of coins spent something between 1500 and 3000 years buried in the earth. Some were buried in pots and were protected to some degree while others were eaten up by corrosion. There are experts in cleaning ancient coins and rank amateurs who ruin 99% of the coins they touch. It is not a matter of whether a coin was cleaned but whether it was cleaned well. Experts can look at a coin and diagnose the best course of action. I'm no expert and buy most of my coins pre-cleaned. Some types of 'dirt' come off with a soak in plain water; some won't budge with nuclear weapons. Some coins sold as uncleaned are known to be in this last category but some are actually unsearched, unsorted and possible to make into a good looking coin. A major point is knowing when to stop cleaning. Really old coins sometimes develop a 'special' surface condition called patina. This should never be cleaned off because it would leave a really ugly surface below and collectors pay a premium for attractively patinated coins rather like US collectors are starting to appreciate colors in early coins. Below are two dupondii of Nero. Both were struck in yellow brass. One is toned but has no patina. It may have been a river find or it may have been cleaned to remove an ugly patina. The other has a green patina. Since the patinated coin also has a bit more wear and less detail, the two coins are probably worth about the same to collectors. Neither would be wanted if they had been struck in 1793 but there is a market for such ugliness from 54-68 AD. I suggest you follow the cleaning instructions and stop cleaning before you get down to metal. Patina can be brown or many colors but relatively few uncleaned coins have premium patinas. Just don't scrub with a wire brush or anything harsh. That dirt took centuries to build up on the coin, have some patience in removing it.
