The SMS Rust Colour Set has been designed specifically to give you the 4 best colour tones to create realistic rust effects on your model. 
 
Airbrush on the Dark Orange Rust Colour first as a base, then go over in a mottling fashion with Light Orange Rust to create a tonal difference. Then with a paint brush, brush on some random splotches using a dark blue colour such as SMS PL71 Insignia Blue and then around the edges of that with Red Rust, Red Oxide or a dark brown colour of your choice. 

Then tie it together with a very light dusting coat of Red Rust or Red Oxide through the air brush and finish up by dry brushing on a mix of SMS Weathering Pigments Earth & Red Earth.
 
Experiment and find out the best way that works for you!

SET CONTAINS 4 COLOURS : 
 
Light Orange Rust 30ml
Dark Orange Rust 30ml
Red Rust 30ml
Red Oxide 30ml