Sa'drok Rawrs - Rust Material

Roughly following along with a YouTube tutorial I hand-rolled this simple rust material from scratch.

A Suzanne monkey with a rust material applied

Material Nodes

The material nodes were laid out into a few groups. This made the view a bit neater and easier to navigate.

Here we have two masks and three layers:

OG Color is the paint layer representing the outer-most layer before rust set in.
Edge represents the “under” layer of the paint as it starts to fade into rust.
Rust is the, well, the rust representation.

Each of these layers output three values:

The Diffuse color that ends up on the Principled BSDF’s Base color
The Roughness value that determines how rough or shiny the surface is.
The Bump Normal is the normal output of the Bump node.

Each of the three layers gets mixed with the next one using two “Big Mixer” instances before having the three mixed set of values plugged into the Principled BSDF. The two masks are plugged into each mixer node and the second one’s factor is also connected to the shader’s Metallic input to differentiate the shading between the rust and the paint layers.

The material nodes laid out in different groups

The paint and rust layers

The three layers are basically the same: A noise texture fed into three color ramps: Diffuse, Roughness, Bump. The Bump node is also added to set the specific layer’s bump strength.

The mask layer

The mask layer is a distorted noise texture with a binary (black and white) output thanks to the Greater Than math node. There is a auxiliary noise texture on the left. The XYZ values are offset by 0.5 to center the zero-to-one range around the zero point. Then it gets added to the incoming texture normal with a bit of scaling to dial in the strength.

The mixer group

Despite being labeled as “Big Mixer”, the group is fairly simple:

A color mixer that mixes the two diffuse color inputs using the mask.
A float mixer for the two roughness inputs.
A vector mixer for the two bump normals.

This creates a harsh edge between the A and B inputs. For the bump an extra edge on the limit of the mask gets added as well.

And that is a fairly simple rust material. Just a few basic nodes connected together to make something promising.

Grab the blend file here