Compared to:
http://www.apug.org/gallery1/showimage.php?i=62981&catid=member&imageuser=13874
This is the first print I pulled from this set of plates, and shows the difference that wiping the plate makes. The less you wipe the ink from the plate the darker the image, and if you wipe different layers at different weights you can change the colour balance. You get about half a stop to a stop's variation each way just with wiping. Creative, yes, easy to standardise if you're aiming for repeatability, no.
You can read more on the process here:
http://www.heavy-arts.com/2011/10/12/3-colour-photogravure/