As said: Fundamentals of Philately by L. N. Williams is a pretty good book, and has good sections on all printing processes.
I picked this one up in a used book store. It says revised edition 1990 (first was 1971). I don't think the previous owner had ever read it, as it cracked open as for the first time when opened.
It has other uses also. Sometimes when I can't sleep I'll read a few pages. Works every time.
It's a very good book!