Decal over polished base material?

When placing a .png decal to a polished aluminum surface the decal does not inherit the base material polish? What to study?

Currently it is not possible to control decal material properties. This will be done in a future version of Rhino, possibly Rhino 8.

Check my post Emboss a signature on glass - #3 by nathanletwory to see one possible way how to do this with PBR materials.