If I forget copper coins in my pockets when washing they come out shining like new. Also i often use window cleaner to clean thermal paste from heatsiks and the ones that contain vinegar makes them shining like new. So You could use any cleaner that contains acid like window cleaner, batroom cleaner, limescale remover ect. Just dont forget to rinse it well afterwards or it will start coroding very fast. By the way i do have one zalman copper cooler that i do not use I think it is 9500. I will give that a try and post back for You if You are afraid to damage Yours.