How do I clean old copper coins?

you can use Vinigar

How To Clean Copper Coins

If it's just accumulated dirt and stuff, you can try soaking the coins for a couple of days in olive oil to loosen it. If it's anything that you can't remove with the olive oil, leave it alone

Some of the suggestions you've gotten are absolutely the worst thing you could do. Vinegar and ketchup are both acidic. They work by eating away at the surface of the coin, and salt or toothpaste act as abrasives. It works the same way that sandpaper does. Once you've done that, the surface of the coin will never look right again.

Any suggestion along those lines will damage the coin, and kill any collector value. It's not unknown for coins that have been treated that way to lose 90% of their collector value

We just did an experiment in my chemistry class where we had to clean a copper penny. We immersed the copper coin in 6 M nitric acid (HNO3) for less than a second and then rinsed it thoroughly with water before drying it with a paper towel. It's easy and does not damage the coin. Good luck!

If you suspect they are valuable, DON'T clean them yourself have a professional do it. First, wash them off under water lightly, don't SCRUB ! pat dry with a towel

Then get yourself a bottle cap for each coin and put some olive oil in the cap, then drop a coin in each cap and let them sit a few days, or weeks, or months. You have to be really careful copper is among the most chemically active of all coinage metals. If you want to take it a step farther yourself you can get some MS70. A good coin dealer will have it and can tell you how to properly use it.

Polish Your Gold, Don't Clean Your Copper

I did this once for the kids a they found loads while we were out at a park, i just washed the dirt off first then left them to soak in dark malt vinegar overnight... amazingly they came out almost a different colour like brand new.. and some were many years old !

BELIEVE ME THIS WORKS - TRY IT ON A CHEAP COIN FIRST TO SEE THE EFFECT !

1)In a small container, place a small amount of table-salt (1 gram is plenty).

2)Add enough acetic acid (vinegar) to thoroughly moisten all of the salt.

3)Now simply apply the paste to the penny wherever you want it to brighten up. The effect is immediate and obvious.

4)Note: if you don't have any vinegar you can substitute it with Ketchup because it is also acidic. This works well for copper bottom pans, too

Be very careful. Clean vs. polish. You can clean them with soap and water to start. Go ahead a try the suggestions below but realize any obvious polishing attempt reduces their value.

Ketchup has been one of the best copper cleaners that I have ever used. It can take a lot of ketchup if it is very tarnished.

It's better if you do not clean them because if you clean them, they will be damaged and cleaning them can cost you several, dozens, hundreds or even thousands of dollars so it is best to leave them alone.