You will need to get a slide, and there are many kinds to choose from. You’ll need to try out a few different diameters, lengths, and materials to see what suits you best. Most acoustic slide guitarists place the slide on their pinkie, leaving three fingers free for forming chords and fretting single notes without the slide. Placing it on your ring finger lets you grip the slide from both sides, with your middle finger and pinkie, but it leaves you with only two fingers free for chording and fretting without the slide.
Generally, the heavier the slide, the better the tone, with a higher “note-to-buzz” ratio. At the same time, a heavier slide is harder to manipulate—there’s more to move around, and if your guitar still has relatively light strings or low action, it’s going to take more finesse to keep a heavier slide from bumping into the fretboard. But weight is just part of an equation that also includes what the slide is made out of.
The two classic slide materials are glass and metal. Some of the first slides were made from the tops of wine bottles (hence the term bottleneck guitar) or from lengths of pipe (hence the term . . . er . . . metal slide). Glass tends to have a smoother, rounder sound; the distinction is particularly noticeable on the lower, wound strings, where a metal slide can get really raspy. A thick and hefty brass slide will have more smoothness to it but can be a lot of weight to haul around the fretboard at first. Thin-walled glass slides will just sound plinky, with almost zero sustain, and thin metal slides, usually steel with a chrome coating, will be equally difficult to coax a great sound from. If you’ve been using one of these, yes, you can blame your gear.
Ceramic and porcelain slides are a more recent development, offering the best of both glass and metal: they’re smooth and relatively light like glass, but they feel denser and offer a touch and sustain more reminiscent of metal. They’re a little on the fragile side, chipping and cracking easily if you don’t take especially good care of them. Meanwhile, there are various small manufacturers making heavy, hand-blown glass slides, slides made from real bottlenecks, and various kinds of tapered and curved brass slides as well, all of which are worth checking out.
As for the size of the slide, it’s easiest to continue to fret chords and single notes if the slide covers just the first two joints of your pinkie. This means finding a slide that fits snugly enough that it comes to a stop right above your second knuckle, yet is long enough to cover all six strings when you lay the slide across the fretboard (see photo at right). Anything longer will just make it that much harder to sense where your finger is inside the slide, which in turn will affect your sense of where to place the slide to cover a particular string or fret. Anything shorter will make it impossible to play a full chord with the slide across all the strings, or to cover bass notes with the slide while playing a melody on top.
Excerpted from Acoustic Guitar Slide Basics