Pure copper is not the best metal for knives. Unless coated, it corrodes relatively quickly when exposed to elements and to the acid from your skin(leaving fingerprints etc.), amongst other things. The patina is a hate it or love it sort of thing. If ya like green - ya like it...but in the humid south where green = mold most the time, it makes it look 'dirty'.
And it's a pain to work with. Copper is a very good conductor and heats up very very fast. It becomes maleable very quickly, and starts to heat color quickly. Even mild grinding by hand to place a bevel or flatten an edge requires wearing thick gloves to protect your hands from the nearly instant heat conducted into the metal even with fine grit belts.
I do copper on occasion for the look. But I am only doing it when people request it. Otherwise I stick with bronze or brass or steel. They look nice, easier to work with, and patinas nice, too.
WYK