I've made progress testing different ways of applying rust to my #Gallowdark scenery (using 5 shades of Vallejo acrylic rust paints). So far I've tried:

1. Painting on the rust, followed by a wash (50:50 Agrax Earthshade:Lahmiam Medium wash) and a light dry brush of leadbelcher
2. Stippling on the rust, plus dry rust pigment added on one side
3. Airbrushing on the rust, followed by a wash

My favourite is the stippled+pigment - the transitions with the airbrush are just too smooth (!)