Modern clad coins turn to crud in a very short time, even away from a salt beach. The good thing is that they clean up pretty easily. There are probably a thousand recipes for cleaning clad in a tumbler, but here is the one I have discovered that seems to work well:
Fill your tumbler about half full of aquarium gravel. Add a handfull of clad coins (be sure you don't mix pennies and silver clad in the same load or your silver will come out copper plated!) then add an about two ounces of white distilled vinegar, a dash of hand soap, and enough water to just cover your coins (at this point your tumbler should be about 5/8 to 3/4 full). Then - and VERY important - you need to add some ammonia to keep the gasses generated during the cleaning process from blowing the lid off your tumbler. I used to use about an ounce of ammonia but finally discovered that it doesn't take that much - in fact, I now just give about 8 or 10 squirts of WINDEX (which is basically a weak solution of ammonia) to my tumber barrel before putting the lid on and tumbling the mix. Some people add a bit of table salt to the mix to speed up the chemical reaction, but I haven't had much luck with salt added. It will take about 3 or 4 hours of tumbling to get your clad looking like it just came from the mint - provided you don't put too much in one load. If you put too much even doubling the tumbling time won't get it completely clean. When you feel the coins have tumbled long enough dump the mixture into a strainer and run clean water over it to rinse very well. I use an old collander I stole from my wife (I bought her a new one). Then pick out your coins from the gravel and put them on a towel to dry - or better yet, dry them on some soft cloth in the sun.
I DO clean my silver the same way - and even throw silver rings, bracelets, etc., right in there with the clad coins. BUT I'm not talking about cleaning a 1916 D dime that way - in fact, if you have a potentially valuable coin, you shouldn't tumble it at all - just wash it in water and DON'T scrub - even with a soft cloth.
Pennies will come clean with the same recipe and in fact take a little less time to become "showroom" fresh. Modern zinc pennies, though, especially if found on the beach, are often not salvagable. Collect enough of them, put in a jar and tata! you have a nice door stop.
Now, what I need is a tumbler to repair those coins the lawn mowers have had their fun with. (After about a dozen years of detecting, I have more than a gallon of these). I tried hammering them back into shape and rolling them up, but found that if those automatic coin counters that the banks use kicks out more than one or two in a roll, they're not going to take them. And your UNCLE will not replace them like they used to. (Remember the days that the banks would repace your torn dollar with a new one as long as you had more than half of the torn dollar - try it today.)
The FED/MINT will take those damaged coins back - but they basically pay you scrap metal rates - and you have to pay shipping to them.
I find it annoying that a country like Mexico can strike base metal coins that still look good after years on the beach, but ours look like crud in a few weeks. Oh well....
