Randy - Thanks for kicking off another fine episode of Weathering Wednesday!
For this edition I have several items: The first two images are of a wooden tunnel portal ( actually it's made of styrofoam ) used on the Mountain Division of my layout. I used flat black spray paint by hold the can at a distance and just giving a squirt here and there. Next I used some spray glue so the edges of the braces ( acting like shelves ) would catch the debris I sprinkled here and there ... as if the bracing had caught some of the stone that had fallen from the above mountain. Of course I made sure the center of the portal got a good dose of flat black to give the effect of decades of steam locomotives entering and exiting. 
Here is a GN boxcar ( by Weaver ) that I weathered using pastel chalks. I wanted to give a dusty look to the car. 
Here's a Santa Fe boxcar where I used Floquit Grimmey Black spray paint held at a distance. This may have been one of the first attempts of weathering using spray paint. I also used pastel chalks ... especially at the bottom of the car to show ballast dust which has been thrown upward from the wheels as the car travels the mainline. 
Here is coil car I weathered. Again using pastel chalks. 
