Be aware that his tunings were 6 string tunings. He doubled 3 strings to make 9 giving him half a 12 string sound, altho' I don't believe, from memory, it was just the top 3 strings he doubled. He used several normal 6 string tunings, with some doubled by octaves, of course. If you search some of the other country blues sites you should find extensive discussions about his set up and some close up picks showing which strings he doubled.
Some other reasons why he doesn't get discussed much are that he played a lot with electric pick-ups/guitars and so is considered outside the realm of discussion by some (that's just wrong!) and because he used a complex right hand technique that isn't easily replicated using the normal opposing thumb to finger(s) style that most use. I believe he learned somewhat from Charley Patton, whose right hand technique you also don't hear discussed much.
: I know that Big Joe Williams experimented with
: additional strings - but why is there such
: little discussion about his technique. I
: would like to find out something about his
: tuning patterns for instance. What do we
: know about the basic business of this top