The black chrome that leica uses is called Eloxal. It is a chromium salt and it is a proprietary process , held by Leica. You can buy the stuff, at a cost, and do it yourself. However, as it involves hydrochoric acid and cyanide + other very toxic chemicals. it is not recommended for "home" experiments!
The surface has to be covered first with a copper layer and the a nickel "sealer" and after that you can "strike" the black chrome. The surface can be glossy, semi-matte and dull matte. It all depends on the treatment of the underlaying surface. If you polish the nickel surface to a high gloss finish, the black chrome will come out glossy black.