Hi, Tooling on dark veg-taned leather is easy, but make the carving outstanding is difficult. If the leather is dark brown, you can still use black antique. But if the carving is on black leather,I think you can only use lighter antique on the project with only knife carving lines. For sheridan style carving. Try to carve deeper and use a round spoon modeling tool poking the back of the leather to make the flower and leaf more stereoscopic. Here is a picture from a japanese magazine, Hope it is helpful.