Explain how you incorporated a material property map here:

We use a grid (black/white) to make the distinctions obvious. It's all or nothing, so the effects are drastic.

The left sphere is a roughness map. The metalness is about 50%. Notice hour the rough areas are purely diffuse, while the other areas are shinier.

The center is a metalness map. The metalness is either 0 or 100%. A metal surface doesn't give its surface color, so the specular highlight stands out more (and the non-highlight is much darker).

The right combines the metalness map and a color map.