Weathering and Rusting on Cylindrical Hoppers

I've weathered a set of 4 Rapido cylindrical covered hoppers belonging to my friend Sean.  After I had worked on a couple of them, he mentioned to me that he liked them when the graphics are worn. I left one the way I had done it, but on the other I stripped away my work, and re-did it with more wear and tear. 

This first car has an overall coating of roadgrime, and just a couple of rust streaks.  (I really have to get to work on ballasting that track.)

The following 3 cars are more weather-worn.  Most of the graphics are faded away, with similar wear to the reporting marks.  The original paint is faded, and over time the weld seams have accumulated grime and developed a bit of dark rust.  There is rust streaking downwards from the walkway supports, and a few rust blisters have begun as well. The wheels and trucks have been given the usual treatment with Camouflage Brown Krylon, with brown and black rust powders to the wheel faces. 

While these 3 cars are weathered similarly, each is somewhat different from the others.

I had a phone call recently from another friend (Chuck), who was telling me about his struggles with creating rust streaks on his models. I tried to explain my process as best I could over the phone, and thought maybe I could try the same thing here.I'm not saying this is the only way, but it's what works for me. The items and method I use are below...

Moving from left to right, Winsor & Newton Water Mixable Oil Colour Burnt Sienna, size 000 brush, a flat brush, a size 00000 brush, and Winsor & Newton Water Mixable Burnt Umber. Just out of the picture is a small pot of tap water.

First, on the sample car is placed a small dab of Burnt Sienna from the 000 brush.

Then moisten the flat brush with the water and give it a quick wipe off on a paper towel, so that it is just barely damp. 

With the flat brush barely damp, draw it straight down from that dab of Burnt Sienna. This will wipe away most of that original dab of paint, creating the vertical streak. You can use weld seams or boxcar ribs as your vertical guide.  And it can be helpful to use your other hand to steady your painting hand.

And lastly, with the finer tip 00000 brush, place a tiny dab of Burnt Umber in the centre of where the streak begins to create the blistered appearance.

If you make a mistake, you can quickly wipe it away with some water and try again.