Moss grows in proximity of exposed surfaces and is more evident where water stagnates;
it was really a challenge to create a complex mask network that automatically filter exposed areas, and has a good behaviour in both small cavities and big concave areas.
Observation, design and fine tuning were essential for this shader.
Rust spreads out eroded parts of metals, usually edges and cavities.
Smart tuning the appropriate edge-detection shader makes possible to auto generate masks for extended and complex geometries.
To achieve dust fx I mixed an overall bigger and more isolated particles shader combined with different kinds and frequency levels of noise to emulate stochastic distribution of dust over surfaces.
It was taken into account especially the behaviour of dust according to gravity, surface grip and cavities.
Dust color changes according to surface orientation to the cam and usually it is not grey
This tries to emulate real dust. Photorealistic at cost of lot of render calculations.
Good for high quality renders of hero objects.