Disclaimer

Red brown coins - Very sparing use of acetone, then the oil, a lot like the red coins, but be very careful of turning the brown areas purple.

Brown coins - Just the oil, unless there is grit on the surface. In that case, a little mild soap and warm water, then the oil.

Green coins - Soak in mineral oil for ages, then use acetone to remove all surface spotting possible. Then recoat with oil and dab with the soft cloth. Will not remove everything, but will make the coin a little more acceptable. This WILL LIKELY turn the coin purple, but that's better than green.

PVC damaged red coins - acetone in liberal amounts, then an oil soak. after the soak, a quick coat of oil with a dab thereafter should completely restore the coin.

PVC damaged Red/brown or brown coins - Same as red except watch the acetone exposure. Beware of purple monster.

VERY LAST RESORT - For really crappy looking coins that have little value left, and do not have surface grime...ones you don't plan on selling - ever....and have little or no wear - use a 3-part mixture of Tarn-X (corrosive), lemon juice (for acid), and water (to dilute), and dip the coin for a couple of seconds. It will turn the coin basically white. Carefully hold the coin (with tongs) about three to five inches over a flame (candle) or cigarette smoke if you do that sort of thing....this will restore some red to the coin. Do not get the coin too hot, or you will find yourself with a wildly toned, very ugly coin. This takes practice to get right.

Before I knew any better, I turned a good deal of common circulating cents into little purple works of art. It took practice on the common stuff to know what to - and what not to use acetone on. Copper can be some of the most difficult stuff to restore the surfaces on. I can say that a quick dash of acetone rolled on with a q-tip (not scrubbed on) then a quick coating of mineral oil dabbed nearly clean afterwards is the best way to restore the surfaces without damaging the color of toned copper coins. Roll-end coins from the old shotgun paper rolls look especially beautiful (to those who like colored coins) once this process is done. I liken it to polishing a good antique piece of furniture with furniture oil. Brings out the color but doesn't change the pigment.

If the coin had luster to begin with, none of the acetone/oil combinations should have any negative effect on luster.

Another tip for cleaning copper coins the right way, then practiced to death on worthless wheat cents, and revised somewhat through this experience....for the black caked dirt/grime around the devices, try this:

A stick of soft wood, preferably a stick from a live tree. Sharpen the stick with an exacto knife, then get the tip wet. Use the stick to carefully trace around the devices to remove the cakes of dirt. Be careful to clean the tip often and to re-sharpen it when dull or dirty. One of the worst things to do in this case is to push dirt around on the coin. Pick and lift the dirt up, do not scrub it around.