I've shot a few carsn and trucks with flattened clear to stay away from the "fresh paint" look. A few of them had faded/patina paint that needed some touch-up before shooting the clear. My favorite mix is Southern Polyurethane's 1:1 Universal Clear with roughly 7% flattener added, very slow activator, and no reducer.
It's more evident in person than in pics, but it looks a lot like well preserved and buffed original paint. I've had multiple people at shows ask if it's original paint, so it's pretty believable.
Straight out of the gun, still wet and glossy.
After curing.
On my dad's '66 C10 he wanted a duller finish, so I used 25% flattener. I think 15-20% would have looked better.
My old '66 was shot with Duplicolor paint shop lacquer, half matte and half gloss. It ended up being costing about the same as SPI but was very tough to spray (dried too fast) and slightly yellowed over time.
