Be sure to agitate the paint often so that the metallic particles stay in suspension.
Just the usual ones that apply to silvers and heavy metalics in general... watch your overlaps to avoid jail bars keep your coats even so you don't get mottled patches and don't put it on to heavy.
on most full size cars I prefer to lay silver over a black base coat. it gives much better coverage and therefore reduces the overall paint thickness. if you are going to clear coat the thing I'd recommend a very light first coat (but not dry) one heavy top coat followed by a final mist coat applied in a random pattern to give an even finish overall. allow it to dry thoroughly between coats and tack cloth it down on all but the final coat before you apply any clear top coat. First clear coat should be misted on (clear coat will alter the finish of the silver so the first coat is very light just to seal everything down). let that dry completely then apply subsequent coats wet>
I've been airbrushing metallics for about 40 years, and have never had the metallic powder or flake clog my airbrush. The metallic powders used in metallic finishes, say, like those used on automobiles, are roughly about 2X the size of the grains of pigments used, so they won't cause a problem.
As for thinning, I thin all my paints, enamels, lacquers, to about the consistency of 2% (butterfat content) milk before airbrushing.
Art Anderson
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.