Good result.
Before I got a decent, fine-line airbrush, I used to do mottles by using a cotton bud, dipped in paint and then wiped off, similar to dry brushing. The tip of the bud was then rotated in contact with the surface to be mottled, the amount of pressure used varying the "depth", and the area of rotation varying the size of the mottle.
This worked well in both 1/48th and 1/72nd scales, and the pics below show the Hasegawa 1/48th scale Bf-109E, built 30 years ago, and brush painted with the mottle done as described.
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