Helmet weathering effects like the edges seen here

[lone violet]

I'm making a little helmet display/desk prop for my friend who likes destiny, so far I'm using this as a way to learn airbrushing, but ive never done the anything that looks like the weathering seen on the raised edges of this helmet here, any cool methods would be very appreciated

[mellow basin]

I would personally say youd want to manually paint it on using stipping, drybrushing, and just edge highlighs

Or you could basecoat in red put down masking or whatnot to do rust effect then paint white and remove the masking