This won't be your typical slide lesson. I will show how you can add more chromatic harmony by fretting behind the slide with your left hand. We’ll also explore the tremendous amount of right-hand dexterity that is needed to pull off this particular type of slide playing, which I’m calling “subtle slide.”
In order to take full advantage of the added notes that are possible by fretting behind the slide, you will need to move the slide to your pinky. When you do, whole new worlds of possibilities will open up. It will also allow you to make three-note chords with the index, middle and ring fingers of the left hand.
In order to make fretting behind the slide work, you’ll need slightly high action and preferably medium-gauge strings or heavier. More mass means bigger tone and more sustain, and the strings won’t be slapping against the slide knocking out the fundamental pitch. Also, you may want to experiment with different slides: brass, chrome plated, glass, clay, Pyrex, etc. I prefer hand-blown thick glass, like off of old wine bottles, because the glass is slightly more porous than modern Pyrex-type glass and thus gives me a better purchase on the strings. It is also thick enough to sustain naturally without really needing a compressor, which many players feel they need when using thinner slides regardless of the material.
When fretting behind the slide, you want allow just enough clearance so the note you are fretting will pass beneath the slide and ring just like normal while the other strings are ringing out above it from the slide.
The right hand is a “co-dampener” along with the behind-the-slide left-hand fingers. This is essentially a classical ponticello technique (using rest strokes) where the string is plucked and stopped by the fingers. For practice, play p, i, m, p, i, m, etc. using free strokes and then with rest strokes and you’ll hear the difference.
The open-D tune that will serve as the backdrop for this lesson, “Hazlehurst,” is a 12-bar blues, but there are enough subtle alterations and chord substitutions that it doesn’t sound like a typical Delta blues (even though I named it after Robert Johnson’s hometown of Hazlehurst, Mississippi).
After grooving on the I chord, D, in Ex. 1, the first use of behind-the-slide fretting occurs in Ex. 2 over the G chord. The slide is fretting the notes at the 5th fret with the index finger fretting the 3rd fret of the B string. This gives us an added 4th ringing against the 3rd and root of the chord. The same technique is repeated in Ex. 3 to end the first chorus.
Things are a little more advanced in the second chorus [Ex. 4]. Notice that in Ex. 5 there is a diminished chord (C#dim7) leading into the IV chord (G) and then two more (G#dim7 and Bdim7) getting back into the I chord. The dominant 7 chords in Ex. 6 are then achieved by using the index finger behind the slide two frets down on the fourth string. Finally, in Ex. 7, there is some cool reharmonization and a Gm chord that is made by fretting the third string one fret behind the slide at the 5th fret.