Originally Posted by jammerrs

Firstly you will need plastic primer, colour paint, then laquar.

I'd recommend 800+ wet and dry, used wet.

Flat down the area quiet a good way around the area, dry, spray primer, wet flat, dry, colour, laquar, wet flat and polish

Use finer grades the further along the spraying process you are, you may need filler primer depending on how deep the scratch is, in witch case, use after you've flatter the plastic primer down, then flat that down before colour.

One more thing, mask off the area not to be sprayed, try and tie this into lines of the car if possible, note the colour will be more vivid as it's not exactly matched to your car, the whole bumper will need flagging and polishing to help it blend in

This is based on my limited knowledge of spraying so don't take it as gospil