There was a recent topic, "your biggest coin collecting mistake", I believe it was. I posted that my biggest mistake was buying a $1.00 coin for $25.00 dollars. That was pretty bad. But it would have been really bad if I spent thousands of dollars on a worthless coin, like some big time coin investors have. Then again, just the same, I must revise my biggest mistake. It was not buying a worthless coin, which was only one coin, but in trying to clean a bunch of coins, especially when I first started.
I started collecting coins about 4 1/2 years ago, so I am a young whipper snapper compared to some Numista collectors. The first coins that I focused on were U.S. Lincoln wheat backs. I remember trying to make them as shiny I could. First I would wash them, then scrub them, and over time I soaked them in vinegar, lemon juice, and even acetone to get them bright and shiny. I even ran them through the dish washer. I shudder to think how many coins I ruined, coins that I cast into the coin collector's hall of shame. I also ruined a few silver coins by dipping them multiple times. I had some nice shiny silver coins with scratches and hairlines all over them. What a waste. That was probably my biggest mistake, dipping silver coins.
But my biggest obsession, though, was with verdigris. I wanted to do battle against the green copper cancer with my limited skills. Like I was fighting cancer itself. I washed them, scrubbed them with hard bristled tooth brushes in detergent, and soaked them acetone. I dug into the coins with steel picks to remove the verdigris. It was a losing battle. The only smart thing I did was to send an 1839 Isle of Man coin over to Fluke to treat and repair. I learned it is best to leave restoration to the experts. However, I still do clean verdigris coins. But only those that have verdigris which hasn't eaten into the metal yet. A nice cleaning in Dawn detergent with a hard bristled toothbrush works wonders.