The Dirt Node

The dirt map is a texture node typically used to control the appearance of intentional noise or dirt overlaid on a material.

Strength: This is the value/lightness (0.1 to 10) of the overlaying material spread across the map.
Details: This is the density (1 to 100) of the overlaying material at certain angles as tiny specs of it are closely distributed across the constrained areas along the surface of the normal.
Radius: The relative size of the map set against the surface directly visible to the viewer. 100 will lead to almost complete coverage by the overlaying material.
Invert Normal: An added option to invert the normal and overlaying material.
Tolerance: Adjust the tolerance to avoid the black edges on roughly tessellated meshes.