Jack Orion wrote:
Hi there,
first thing you need to do when approaching slide guitar is to get your notes to sound right. Might seem like a fairly commonsensical thing to say, but still a golden rule that applies to any tuning.
You probably know this at that stage, but remember you've got to position your slide right on top of the fret for it to sound right, otherwise the note you play will be out of pitch (mind you, that can certainly create an interesting effect, but not in every situation).
My advice to you would be to try and play a scale using your slide instead of your fretting fingers. For example, play a minor pentatonic scale using only your slide - without sliding at first, just "jump" from one fret to the other with the slide (might be a little tricky at first, so go gently otherwise you'll make a dent in your frets). A great exercise in its own right, used by dobro players.
Once you get that right, you can try and repeat the exercise, but instead of jumping from fret to fret, you can try and slide from one note to the other (still keeping in mind that it's absolutely vital to be spot on).
So, there you've got it basically. Now, you can try and do the same thing but instead of just playing one note at a time, try to play a chord - as if your slide were, say, your index finger playing a barred chord.
As said previously, all the above applies to any tuning. Keep in mind that Rory Gallagher surely played a lot of slide in standard tuning (although he did play in open tunings as well, most notably open D and open G). What I wouldn't recommend, though, if you wanna try out open tunings is not to detune and retune your guitar too often, as this would certainly damage the neck of your guitar over time, so don't do it too often.
Hope this helps.
Best of luck!
"If the future isn't bright, at least it's colourful"