Scratch the pattern into the steel first with a sheet of coarse grit sandpaper - it’ll give the chemicals a lot more surface area to work with; and it will be immediately apparent, but not glaringly so. You’ll be able to appreciate your own work, without catching the eye of onlookers.
LPT: It’s less immediately obvious, but much more permanent, if you paint with a brush and a mix of vinegar and salt, it’ll seed the rust…
Scratch the pattern into the steel first with a sheet of coarse grit sandpaper - it’ll give the chemicals a lot more surface area to work with; and it will be immediately apparent, but not glaringly so. You’ll be able to appreciate your own work, without catching the eye of onlookers.
Molotov cocktail the vehicle for maximum effect