I recently experimented with some rusty barrels on a diorama and decided I would write a tutorial on it for a couple of reasons: One, so other people can create the same effect should they want to. Two, so I can look it up when I want to do so again in the future and can remember how it’s done.
Equipment: Typhus Corrosion, Skagg Brown, Jokero Orange, Leadbelcher, Agrax Earthshade, Nihilakh Oxide.
I have used a wall for this, but it would work well on pipes or anything that might get rusty!
Step 1:

Paint the entire surface with Typhus Corrosion – this will add the rusty texture which we need for the next steps.
Step 2:

Drybrush with Skagg brown – those texture areas will start to show up in this and the next steps.
Step 3:

Looking a bit corroded there.
Step 4:

Stipple on silver, or other metallic colour, to show fresh chips in the rust.
Step 5:

Use Agrax Earthshade to put in some darker areas where crud might run.
Step 6:

Use Nihilakh Oxide to add a bit of colour to the deeper parts – maybe these were made of copper and are now tarnished!
Finished! Simple way to make an effective rust pattern!
