How to add imperfections to the Principled BSDF Shader (Cycles)? I am looking to create scratches, swipes, brushes, similar to the reference image provided, that will only appear where I wish them to (as shown below).



What is the best Node Group/Layout/Structure/Workflow to implement such scratches/brushes (purely) on top of a material?

For clarity, I have provided the reference image below, as well as the blend file, with the texture in the node setup.
http://pasteall.org/blend/index.php?id=47820

I also dispose of materials from Poliigon, if that is of assistance.
Just add mix rgb (screen) node to your roughnes map and connect surface imperfection map to the second socket