Be very careful how you clean old copper coins. I’m of the camp of just scratching the dirt off with a toothpick and maybe rub a little oil from your forehead to bring out the highlights. The coin below was kept by the home owner and cleaned with hot sauce despite my warnings not to clean it. It is a large date 1803 Flowing Hair Cent but luckily was not the small fraction rare worth $$$.
I suggest you watch this video.