Nickel silver is an alloy of copper and nickel --brass is copper/ zinc---bronze is copper/ tin they all have similar properties as far as machinability with nickel silver being the hardest of the lot and used in the finer ferrules and reel seats. Aluminum and its alloys tarnish quickly and are quite soft. Anodizing is a process done to aluminum to increase its surface hardness and protect its surface from oxidation.