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Just got into the animation lab, nabbed the last available computer station with a graphics tablet and added this little afterthought: if this temple has been sitting in a dense, humid jungle, wouldn't there be growth on the stone? So I dropped the file into Photoshop and added an extra layer under all the shading & highlights and put in some moss. The professor has yet to see this, so I might update this with the result of his critique and a possible updated version.
UPDATE: Prof's review.
Natural looking: not so much. Some of the brushwork is too patterned and lost some of it's painterly look. Gonna have to look up some links, and go for another back-breaking evening at home adding more detail to this until it's perfected.