If I understand correctly, then I think the problem is simply that it's a black material. If you think about it in code lighting looking something like this: ColorOfLight * ColorOfMaterial. If you're like is {1,1,1} but you're material is {0,0,0}, you're always going to get {0,0,0} out.
If you use an alternate shader like Specular, however then you can change the reflection color for the specular part and get a "shiny black metal". This is closer to what happens usually in the real world when you have a black material. There are anisotropic factors that make the material not perfectly black in every direction.
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