We all know that edges in nature are not always perfectly sharp and crisp. On the other hand, not every edge is a big fuzzy blur. Oftentimes, edges (transitions) are between hard and soft.
Freehand airbrushing will create edges that can be too soft, and stencils can create edges that are too sharp. We need an easy way to create intermediate edges.
The easiest solution.
The fix is quite simple, actually. If you elevate your stencil slightly, you can allow some underspray to soften the edge, thus achieving a more natural look in many cases. You can elevate your stencil with various objects, such as coins, pencils, tape, etc., but did you know that some texture stencils come with a built-in elevation? Sure enough, examine the "rough" side of a stencil, and you will see that when placed face down, it raises the stencil ever-so-slightly to create an elevated mask.
It just so happens that many stencils arrive with a rough side. Most people mistake this as shavings from when the stencil was originally cut, and attempt to remove the shavings with sandpaper. However, you'll want to refrain from sanding your stencils smooth. A stencil with one rough side will elevate the stencil slightly, so if you want an easy way to slightly soften edges, you can use this to your advantage. By leaving the shavings attached to the stencil, you have a built-in elevation that will help reduce the severity of some edges in your future projects.
If you need a hard edge, all you need to do is turn over the stencil so that the smooth side is in contact with the painting surface. The closer the stencil edges are to the surface, the sharper the results.
That's it. Good luck with your airbrushing!