What kind of weathering do you want to do?
chipped of paint
Spray aluminium color on the model first
Next spray a protecting coat of future or thin varnish when it's dry.
Spray your wanted color on when this all has dried for 24h.
Let the base coat dry for about 7-9 hours, lightly press a piece of tape on the place you want chipped-off paint
Pull off the tape by a swift and fast manoeuvre
If no paint lets loose, try pressing the tape on harder.
(the coat of future prevents the aluminium coat gets cipped off too)
Highlighted panel lines
Mix some chalkboard-chalk with a drop of dish-washing stuff (forgot the english name) and some drops of water to get a nice thick solution of fluid chalk
Brush on the chalk solution on the panel lines, let it dry for a minute or two, and whipe it off (to the direction of airflow!) with a piece of tissue
You'll whipe off the excess chalk and leave the most of it in the panel lines
Use the right color of chalk though!
Dry brushing is a great way to get metallic looks,
Paint the 'metal' part the colour you want, then drybrush it with aluminium colour, you'll get a nice 'weathered' look
