If you are spraying enamel, there is a special pot you scoop full of the paint/thinners mix and time how long it takes to flow through, to the 0.5 secs, it's that much of a pain in the arse. If you aren't that fussed with the shine and finish, you can guestimate the mix, but it you want it to look magic off the gun, you gotta do it by the numbers, quality paint, top quality thinners, a gun that sprays a perfect pattern, a water trap for the airline, the compressor drain plug loose so the water/air leaks out constantly....... there is nothing easy about getting a magic finish with enamel.... but it's the cheapest paint by far.
Next comes acrylic, lots of coats, stir the paint with a flat paddle like a school ruler, let the paint run off, it should flow off reasonably quickly yet leave a colour coating on the rule, the drips should have very short tails, no tail, it's too thin but lots of coats with a 15 mins plus between them and you can get away with it, long tail, it's too thick and it will dry with an orange peel finish. Just enough air to get the paint out of the gun and evenly spread across the width of the fan, too much air/ not enough paint, a dust finish, not enough air/too much paint, more runs than Bradman. It will never be shiny off the gun, that comes after hrs of buffing.
Polyurethane, Use the right thinners, get the mix right, paints like magic, to get that glass shine finish, the last clean up of the paint pot/gun, 50% thinners, light coat all over, not enough to form runs but enough to remelt just the surface, a better shine than 2 pk, just not as tough.
Gravity feed guns are great for vertical and down hand, but you just can't do that edge from the ground up unless you are very experienced, but by far the easiest to get a good finish, suction guns with the locking pot, make sure the vent hose is clear and paint will not enter the vent hose when you are painting at the angle you need, you may need to spin every thing around to get the vent on the high side of the paint in the pot. Hi volume/low pressure guns, you wanna be good to avoid the Bradman finish with those babies
T1 Terry