Copper does not become a call surface, unitl it hits a call makers Hands Mike, so in reality, it is all, about the call maker.
You can not judge the sounds of a copper call, until it hits the hands of a tried and True call maker of friction.
My meaning is, you can make 5 pots from novice friction call makers, and everyone will probably say, I am not so much into the copper.
Put that copper in the hands of a Experienced Friction maker, and the " Tunes " will change.
Copper has its place in the woods as do many. Ya never know WHAT, the Old man wants to hear that day. All about HIS Mood, what he wants to hear, wednesday, may be slate, thursday, may be copper.
Copper has its place in the woods, Killed to many birds to not have.