yes, I suppose you could, but it'd be a bit of a pain to position it perfectly on yuor texture map. Instead you just make the large texture map and the map 'compiler' (for want of a better word) would then alpha it out to reveal mateal wherever on the metalmap a certain threshold was met.Can't you already make this using photoshop, the texture of the ground, one texture with the same size of metal, and making an alpha mask with the metalmap in greyscale?
Rightfield. You seem to be under a certain misimpression. If I could draw I wouldn't be using photoshop.
Oh, and I used: rendering clouds, layers, motion blur, more layers, edge detect, colour inversion, craclquer and some colour levels fiddling (off the top of my head, I may have used more). It's not just one filter.