Crossroads is played in open G guitar tuning with a bottleneck, or slide.
Arguably one of the most definitive Delta blues songs, Crossroads is basically a version a traditional song, Walkin' Blues, performed by many blues men - notably Muddy Waters, Son House and Robert Johnson. A slide is used to create that plaintive sound and although many have tried, very few have captured that special emotional impact of Johnson's original recording.
Some old school slide guitar players actually use a real bottleneck, but this is mostly for effect and has no real significance except that the old blues guys made use of them. others used a knife of similar to make that eerie sound.
Modern bottlenecks come in a couple of flavors - either glass or metal. For me, the glass type make a warmer sound, and the thickness of the glass wall is important.
A thicker wall means a heavier bottleneck, so when we rapidly move our fretting hand to get that vibrato sound, the heavier slide changes the speed of the vibrato slightly, making for a nicer sound. Just my two cents worth.
The bottleneck technique itself is one of those guitar playing paradoxes.
It's very easy to get the basic action down, but takes a lot more time to control the hand movements so that it sounds nice. If we don't control that bottleneck properly, it turns into a messy sound of glass on metal and isn't very nice to hear, becoming harsh and discordant.
Done properly, however, the technique can produce a warm sounds that just shouts 'delta blues'. Some players make it sound sweet (Robert Johnson, Muddy Waters) and others play it in a powerful, percussive way (Son House).
Accuracy is the key, of course. We need to hit that note, and we don't have a fret to help us, as the bottleneck floats above the frets and doesn't touch them. Luckily, we can aim for the fret we want and then vibrate the slide until we hit it, which is one of the characteristics of the style.
This is probably one of the reasons why bottleneck blues guitar was so popular in the beginning. In the Delta it was hot and humid and wooden guitars were difficult to keep in tune - it was easier to tune down to open G and easier to hit notes using a slide.
Just remember to damp the strings between the bottleneck and the guitar headstock with a finger. If not, you will hear sounds from the strings both sides of the slide and it'll sound horrible!
Open G is very easy to achieve - the bass E string is brought down to D, the A string to G, and the high E string tuned down to D also - that's it! Strum it and you have a G chord. Other chords can be formed but they are not really necessary for this song - Johnson uses mostly single strings and half chords, which are fully tabulated in the lesson. Bringing the Bass E down to D introduces a powerful low bass drone effect and I often use Open D and dropped D for just that reason - it gives a low notes to offset fancy treble work.
AS WITH MOST ROBERT JOHNSON PIECES, ATTACK IS VERY IMPORTANT - CROSSROADS TUITION.
What do I mean by attack? Well, for example, you can slide up to a note slow or fast, and also change the speed of the vibrato when you get there. It all adds to the overall effect. In some cases, when we move on from one note to the next, the change is so fast that there isn't really any vibrato to speak of.
In these cases you need to be very accurate when sliding up to the note. This happens in Crossroads at the beginning of the verses, when we slide up to the 12th fret and then quickly move down to the 3rd fret for a three beat run down, fretting with our finger on two bass strings.
It's a great contrast, playing the low bass run down just after the high treble notes on the 12th fret. It's like a call and answer structure, which has a powerful effect on the emotions of the listener.
