Damir, it's done with the usual "Salting" method using two varieties of salt and baking powder: kosher, regular table, and baking soda. You mix all three together, and then you lay down a basecoat color over your primer. Say a rust color. After it dries, you spritz some water and sprinkle the salt where you want some rust to show . . . wait for it to dry or speed up the process with a hairdryer, then paint your final color coat. Remove salt and VOILA: Rust, chipping, mapping . . . you name it, your paintjobs are going to change for the better.
Plus it's blast to do. Have fun and enjoy the process.