Only if they are bare copper. It is very beneficial with bare copper. It is pointless and not necessary with nickel plating. I would recommend avoiding bare copper for anything, but especially liquid metal application. It's not harmful to copper, but the absorption is just an added hassle that you avoid with nickel. Even when you are not using liquid metal the bare copper starts looking pretty nasty with normal use and keeping it looking sharp is a real pain in the butt. It looks nice when it is new, but looks horrible when it begins to tarnish.