I've gone through the zam threads and found one post which the person used an eraser to get the weathered look. Another used sandpaper to rough up the leather. What else did they use to give the grimy appearance? Dark dirt, paint, charcoal.. any other ideas out there to toss around the forum?
And I almost forgot, the best one!! A partial quote from JDFett:
"process you may ask? well started with some purple around the edges...then in the stain areas went with a little cordovan....then finished the whole thing with burgundy...then the fun...took it outside and beat the snot out of it on the front cement stairs, took a razor to the brim, holding it flat against them brim and scrapped off down to almost the leather color."
Beat the snot out of it! Awesome! In all seriousness, he did use dirt, and alot of color variations too.