So far as the color of the grime/weathering, for what it\'s worth it looks about the same shade as GW Graveyard Earth.
I\'ve found that if you apply \"dirt\" colors in thinned down glazes, or even do controlled drybrushing onto the figure lightly using paint that\'s already at a \"glaze\" or at least \"milk-consistency\" amount of thinning, you can get really subtle weathering effects.
Maybe not the best example, as I didn\'t go \"over the top\" in weathering him, but if you look around the hem of his robes at ground level, you can see my own example here: http://www.coolminiornot.com/183383
Have you sent a PM to the artist to ask, by any chance? I\'d be interested in seeing the reply.