I have had good results for some years using
Tamiya Gloss Spray Paint. It comes in a spray can:
Hold the can about 10 inches away from the part and keep it moving.
I first prime the part using ordinary grey primer, left to thoroughly dry. Then a light spray from the chosen gloss spray paint, enough to cover the primer fairly well but no more. Leave to dry for 24 hours or more in a warm place at room temperature (not a garage or shed in winter). Then a second, thicker coat is sprayed to very nearly completely cover the primer but by no means glossy, and left to dry thoroughly for over 24 hours. Finally, and this is the tricky part, spray the final coat until it looks wet (therefore glossy) and continuous but avoid runs or sagging areas of over-sprayed paint. Make more than one pass of the spray and as necessary, coming back to selected areas again to apply more paint as needed. This final coat dries in 15 to 20 minutes sufficiently to prevent the risk of runs after that period.
The reason for the quite long drying times is that the propellant gas dissolves in the paint in the can. This must be allowed time to pass through a layer of paint (especially the final coat), otherwise the final coat will not be glossy.
Assuming no runs as a result of the final spraying, it is important to orient the newly sprayed part to minimize the amount of surface area at any one time which is vertical and therefore prone to run even after spraying. This is difficult with a part with several areas at angles to each other. Until the drying time of 15 to 20 minutes is up, keep the part rotating to avoid runs. Dust has never been a problem for me.
But some parts will always have an area that is vertical and which could run as it is left to dry. An example is the bonnet (engine compartment cover) in the white tractor (below). To avoid that with these difficult parts I stick a piece of White Tack to form a handle and sit patiently rotating my wrist and therefore holding the part in different orientations to prevent any runs gathering speed. I have bought a tiny motor and will make a "machine"which will rotate the part at one revs. per 4 seconds while I have a cup of tea.
The application of the final coat, to wetness but no further, and the minimization of post-spraying runs, need practice on scrap test pieces, even going to the length of gluing up some test pieces from poly sheet with lots of surfaces at different angles to each other. A rub with a cloth and a polish (the type that is ever so slightly abrasive, not a wax polish) can be used when the final coat is hard (a few days later). A final wax polish can be done.
It is quite tricky but once mastered the result is consistent. One advantage (apart from getting a good gloss with this method) is that there is no cleaning of an
airbrush. However, for parts with deep recesses it is possible to decant the spray paint and shoot it through an
airbrush, but clean it very thoroughly after.
Here are two of my efforts (1:24). The truck, being white, doesn't in fact show gloss very well when photographed, but some reflection can be seen near the far corner of the cab top.
In the Roll-Royce, the rear right mudguard shows slight orange peeling which comes from not applying enough final gloss paint. Orange peel will not sand and polish out. The rest of the model paint is perfect, with no orange peel, and good reflections can be seen in the photo.