I have some Japanese coins dating back over approximately 100 years. Some of them are very well weathered/tarnished. I am considering selling them, and wondering whether I should clean/polish them before putting them up for sale.
Will they be considered more valuable with their patina intact, or with the shiny look of a brand-new coin?
The general rule is that you shouldn’t clean old coins. Most non-professionals will due it wrong, damaging the coin and reducing its value. And there’s no point in cleaning off the patina - it is part of the coin. Old coins are valuable because they are old, not because they are shiny.
This article recommends only using water and a soft cloth if you must touch them up.
Don’t clean them–period/full stop. This from a professional numismatist.
Retired but seconded.
Don’t you watch Pawn Stars or any other show like that? Never clean coins or anything else old!!!
You have to realize that patina, or toning, isn’t something that’s been added to the surface, like grime. It IS the surface, and to remove it is to remove the actual surface of the coin. Do you really think that what’s remaining will have the original luster of a new coin? Don’t do it.
Oh, and many collectors specifically seek out coins that have interesting patina, especially what’s known as “rainbow” toning.
These (scroll down) are some extreme examples, but toning on coins can be really quite striking and beautiful and add to the overall desirability.
I talked to a numismatist about this once. My point was that given a coin had been rattling around in pockets with other change for decades, that you could still see if it had been gently cleaned with a soft cloth? He simply replied, “Absolutely.”
Dennis T
I’m not any sort of numismatist, so no, I don’t know these things at all. My only experience in this area involves childhood experiments in cleaning pennies with vinegar, which I recall left pretty shiny-looking copper.
Anyway, message received, thanks to all who contributed; I will refrain from cleaning any of these coins before sale.
The tale of an 1850 double eagle: a guy buys an 1850 gold $20 double eagle for $102,000. He cleaned and polished it to a mirror like finish. Turned something worth about $250,000 into something worth $10,000.
Those would be so pretty if someone just buffed the silver spots off. 
Seriously, those are some beautiful unicorns.
Since you mentioned that show, I always felt they were a great bad example. They always say don’t and then they turn all this stuff over to that restoration guy who cleans and repaints it to the point I would never want it. OK – it isn’t coins; but the same holds true for a lot of the other things they have butchered for them too.
Coin collector from the age of 10, and granddaughter of a journalist who had a syndicated column on money and coins in the 70s.
Coins should be cleaned only it they have actual mud or something on them, and then very carefully with distilled water and a very soft cloth used to blot, not rub. It’s very tricky, because you want to get the grime off WITHOUT getting the tarnish/patina off, or scratching the coin.
Sounds like what you have should under no circumstances be cleaned.
This reminds me of a story told long ago on a usenet coin group. A guy inherits a pile of Morgan dollars, arranges a meeting with a coin dealer (the dealer was the one telling the story.) Dealer finds out that a friend had told the guy to polish up the coins really well to make them as valuable as possible. Dealer tells guy that the coins are now worthless as collector’s items and are worth pretty much their melt value. Guy assumes that dealer is attempting to rip him off, storms off in a huff.
Later on, the guy contacts the dealer again, to tell him that he wished he had believed what he was told. Turns out that after the meeting, the guy subscribed to one of the slabbing services, which charges an up front fee plus a per coin fee for grading them. With the number of coins he had, the fee for grading all the Morgans was in the high hundreds or low thousands (I don’t remember exactly.) Every coin came back labeled as “cleaned, ungradable.”
It isn’t just collectable coins, many antiques or collectibles have had their value seriously diminished by well meaning folks who try to spiffy things up with a whiz-wheel or coat of paint, varnish etc. Toys and guitars for example. The rule is, “leave it alone”, if somebody is interested in buying your newfound Treasure, they’ll know what it is and what to do with it, what not to do with it.
Olive oil has been used to clean ancient Roman coins, not really “cleaning” as in popular usage, actually soaking for long periods of time. Don’t know how that factors, I’d think that would be harmless enough.
Harmless. Improves the coins perhaps 10-25%.
And violins. Back when I was in middle school, I “improved” my fiddle with a coat of varnish. Had to get a new one.