Great suggestions here. Seems I've got my work cut out for me.

I've been giving the G tuning a go. It's interesting how lost you feel when you've become accustomed to one or two tunings over quite a period of time. Funny you should say the G tuning suits Robert Johnson's stuff. I've learned many of them in the D tuning (Really just an open E tuning one step down). To me the G sounds the more sombre.

I think a big part is the ear; what you're more accustomed to hearing. What got me going on this was all these bluegrass players I've been hearing lately, and these beautiful lines they play over these tunes. But my mind can't quite think in those terms yet. Still more blues rather than bluegrass.

As far as brass vs glass, vs chrome, it kind of depends on the axe and the tune. glass is great for my Strat when I'm looking for a softer tone, but if I really want to get nasty the ol' chrome slide cuts very nicely. On acoustic I tend to go brass for softer stuff and chrome for more edge.

And Gerald, don't let a "lack" of slide guitars stop you. Find some old beater of a guitar (ie one that holds its tuning, but maybe the action's too high, etc.) and just tune it to an open tuning like D (or G!) and leave it there and pick er up once in a while and give it a go. I started with some RJ tunes, as well as some things like Sentimental Journey or amazing Grace (ala Rod Stewart's "Every Picture ... album). SB