There is a strong tradition in using slide guitar for the blues. Slide guitar became a stylistic choice over fretted guitar by players who didn’t have the skills or patience to fret the guitar and found it easier to slide a smooth, rounded object over the strings to achieve a similar effect. But whatever its origin, slide guitar is a staple of the acoustic blues guitar sound unlikely to ever be imitated by synthetic, digital means.
However, for the greatest practitioners, such as Charlie Patton, Sylvester Weaver, Blind Willie Johnson, Son House, and Robert Johnson, slide guitar was an unparalleled mode of expression evocative of the human voice as well as the wail of train whistles — a sound near and dear to country blues guitarists.
Early, rural-dwelling slide players used anything they could find to produce the slide effect. The edge of a pocketknife, a length of pipe, and a medicine bottle were among some of the top “tools” used, but the most popular was a broken bottleneck (minus the sharp edges, of course). Because the bottleneck was probably the most popular, slide blues guitar is sometimes called bottleneck guitar.
These days, you acquire your slippery weapon of choice by going to a music store and selecting from the pre-packaged slides in the display case. Metal and glass tubes are the two most common styles (though prepared bottlenecks are available, too) and come in various diameters to fit different-sized fingers.
Metal slides, especially those made from brass, are heavier (they have more mass), bolder-sounding, and provide better sustain, but they’re more difficult to master.
Credit: http://www.jimdunlop.comThe heavier the metal slide, the bolder the sound produced.Glass slides are light and have a rounder, mellower tone.
Credit: http://www.jimdunlop.comGlass slides have long been favored by blues greats for their smooth sound.