And about how Hokusai watched the printing process - will give here an example. Let them be the same Red Fuji, if nothing about it it came from the collection of the Boston MFA:
http://www.mfa.org/collections/searc...x=0&submit.y=0
They have a collection of six prints, and easy to see that among them there are no two identical (even if we discard the third, which is a side option, imprinted with the other blocks). The boundary between red and green dancing totally unpredictable way, never the author of such would not be allowed, if the process is actually controlled. But in reality it is only noted in black and white a print 2 colors, and an indication of a smooth transition from one to another. Next - art printer ...