Don't expect to get the same "fresh from the factory" finish with an aerosol can. They CAN be used to achieve satisfactory results on older cars, but be aware that car manufacturers actually use many different shades for the same colour. Vauxhall used to use a blue called China Blue, this had about 14 different shades! The off-the shelf aerosols are usually "somewhere in between" the shades.
If the laquer is peeling, flat the whole bonnet down using 240 grit wet & dry. Its important to feather back the peeled edges of the existing laquer, even better to sand off all the laquer. Do all this with the bonnet closed & don't miss any. Add a bit of shower gel to the water in the bucket to stop the wet & dry clogging the paper. Then use 400 grit wet & dry & do the whole thing again to remove any coarse scratches left by the 240. Open the bonnet & flat the returns lightly with the 400 grit.
Now wash it down with clean water & let it dry. Can you see any shiney bits? There the bits you missed, go back & flat them with the 400 grit!
Wash down, let it dry & mask up anything you don't want painting (use good quality masking tape). Now give the bonnet four coats of grey primer, let it touch dry between coats. Next spray a very fine mist of black over the bonnet (guide coat) & let it dry. Now CAREFULLY flat the primer using 600 grit wet & dry. All you are aiming to do is remove the black mist, leaving a perfectly smooth surface.
Wash it down & re-mask if necessary.
Using the previous good advice, warm the paint in warm water (dry the cans & shake well before use). Using even passes, start to spray the colour coats, start at the top of the bonnet & work to the front edge, each pass should slightly overlap the last. Three coats will be adequate, letting each coat touch dry to allow the solvents to evaporate.
Stand back, does it look okay with the metallic nice and even? Now you can laquer it. Four coats is fine, but be aware that because its difficult to see the laquer (because its clear) its very easy to be heavy handed & put too much on & cause runs in it. If that does happen, let the run dry completely & flat it out using 1200 then 1500 wet & dry before cutting & polishing.
(i'm too impatient for spraying!) and it came out fine. as i understand it you have to rub the whole thing down to make sure there's no lacquer left and then make sure it's really cleaned of dust etc. then slowly build up with fine layers until you get an good even coating.
