I'd have thought so.
How about chemically blackening the copper ? Or a black solder resist?
With emissivity the apparent color is not as important as the
surface quality.
We painted our black body calibration sources with a matte black
paint and got near .98 plus emissivity. Average Human skin is also at
..98
Both are due to surface texture. The bare aluminum ingot has a smooth
surface, and some of the IR generated inside when it gets heated get
reflected back inside. When it has the matte finish, it has many many
more angles to radiate from the surface at. They are little tiny
scratches that add up to more actual surface.
IR and a smooth, polished , flat surface do not get along. It
reflects back inside the medium, and any that does radiate only
radiates from the surface in a perpendicular ray. The matte surface
allows the heat in the medium to radiate away from its surface at
several angles of incidence. A denser IR "flux" emanates.