Settling Dust

Aging and distressing the low/underside of objects can be visually appealing and fairly easy to apply. (Not to mention easier to reach than the top - and I know what it's like to hunt for a 16' ladder at 2am in a deserted building.)

However, this photo provides a nice opportunity to examine how airbourne particles settle on a horizontal surface. The bottom of the pipe is rusting, but fairly clean. The top is covered in black exhaust.

So it doesn't hurt to occasionally think like a dust bunny:  find the horizontal surfaces and let gravity influence your airbourne aging.