Andras, Thanks for the kudos. Not a problem describing the weathering process. For the paint chips I use a couple of methods. For rusted chips I use a small brush and aplly irregular patches of Vallejo 872 Chocolate Brown, or 822 SS Camo Black Brown. I find these to be a good match for older rusted areas. Once dry I use a very thin wash of Burnt Sienna oil paint (Tube type) touched to the Vallejo paint. It will spider out and give a nice effect. For the other method, ie. newer, less sever chips, I use some Model Master flat black and some Titanium White, also a tube oils paint. I mix this as a dark gray to light gray color. Again using a very small brush, I apply it randomly where rocks and other debris would be thrown up by the tracks, and to other areas prone to contact.
*** I do all of this after the tank has been gloss coated, decaled, and then flat coated***
The streaks that represent rust and dirt are done with Burnt Umber and Raw Sienna oil paints. Small amounts are again applied with a small brush and allowed to set for a few minutes. I then use another dry brush and pull the paint downward repeatedly until I get the look I want.
I follow all of this with pastels along the lower half of the skirts, or hull area. It will cover up the paint chips slightly, which is what I try to achieve. The scratches are done over the pastels using a toothpick.
That's pretty much the gist of how I do it. Let me know if you need more info. Hope it helps. Thanks. "Q"