black/dark diffuse, high specl with high gloss...and the main thing is reflection, so depending on whatever you are rendering in, take a look at how to do reflections.
You can also put in some variations in your specular map to achieve a slight dirty look. Just blend in a tilable concrete texture with a low contrast .
Unreal and Unity are good in rendering Reflections in Realtime, so if these are your target engines you could get good results when using a cubemap.
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Unreal and Unity are good in rendering Reflections in Realtime, so if these are your target engines you could get good results when using a cubemap.