My 2 cents, simple texture maps won't cut it for metal.
I use purely procedural textures, but bitmap equivalents for the following also work :
- Good high contrast reflection environment is essential, preferably HDRI, or multiple lamps with different intensities and colours. But a black background with bright white stripes usually works.
- Bump map with a subtle dot/pit pattern, about 0.2mm pit size, 5-10% coverage
- Color map : dark grey/black with white spots and stripes
- Reflection amount, light grey (85%) with black spots and stripes
- Some blurring on the reflection always helps
- Reflection color might be toch reddish, because of the bronze.
And for rendering, Global Illumination and Caustics work wonders.
It is far from perfect, I'm still tweaking it a lot.
Example 1 - Quark
Example 2 - ring
The whole dots and pits should be more pronounced and abundant in occluded and internal areas, since IRL they can't polish there.
Hope this helps you and others with the metal renderings !
Virtox / Stijn