Rusted Metal

This material is an example of rusted metal (or alloy) with principled shader.
The “rust generator” node group generates a map and normals for the rust,the explanation of the parameters of this node can be found at link
To create rust color i’ve used the “multiple color ramp” node,that allows you to decide colors and position points ,using input parameters,increasing flexibility.
Up to 5 colors can be chosen. The node can be obviously modified to accept more colors

The image,an ancient bronze elm:

The multiple ramp node:

The blend file:
elm.blend (1.9 MB)