A lot of people have been asking me how I did the weathering on my armor. The weathering was done using the sponge/rag technique. First, I would take black acrylic and dab it with a sponge and rub it all over the armor,section by section, covering every square inch. Then, after letting it sit for a moment, I would rub it off with a rag. If I wanted to remove more, I would wet the rag. Then I would repeat the process with brown acrylic. Then, after all said and done, the streaks and edges were done with a silver leafing pen.
A word on getting "that look". The point of weathering is that the armor does not look brand spanking new. You shouldn't weather your armor with a specific pattern in mind (unless you are airbrushing and are very skilled). The point of dirt and wear and tear is that it is supposed to be random, so don't fret if the weathering deviates from what you envisioned. But, you should take into account of things like gravity, where the bottom might be more dirtier than the top, and edges and crevices, where dirt would most likely settle in crevices, and that edges would definitely almost always have those silver 'cracks' in the paint.
I am also a huge fan for natural weathering. One technique I would like to share is if you are ever doing an armor piece, use a metallic dark steel spraypaint w/ primer, and go over the entire armor two times. Then paint over it the color you want, and don't seal. What you will get is that if the paint on the outside layer starts to chip or fade, you will see the dark steel base paint underneath, like in real life. Of course, if the paint starts coming off too much, then you should seal over it again once you get the look you want.
This is only my weathering philosophy, as many other very successful and accomplished cosplayers might have different philosophies concerning weathering, as there really is no wrong way, such as blackwashing, drybrushing, airbrushing, etc.