Factory finish is duracoat, just polished if it has a slick/smooth finish.
If the pistol is already coated, then you can strip the finish with acetone (soak and rub if you want to take all the finish off if cracked), and just recoat over the already prep'd steel surface.
As for touching up Duracoat scratch finishes, use a little acetone on a cotton cleaning patch, and just feather out the scratch so there is not sharp edges (think of it as wet sanding), then you can touch up the finish with a fresh coat.
As for having a slick finish with Duracoat, thin down the mix (20%) with the air pressure low and the feed high on the air brush (gravity feed cup gun works better).
or, if needed, run a thicker coat, let if dry for a couple of days to allow the poly to set up, then go back and use a little acetone on the patch to polish (wet sand) or take the coated parts to a polishing wheel.
For a more anodized/parkerized type looking finish, run the mix without thinning, turn the air up, and run the feed low. Get the light base coat down, then pull the air brush back and then give the surfaces a final fog coat .