The first thing to do in putting together your own 12 bar blues in open G major tuning is to set your guitar tune to G major. Change the tuning from EADGBE to GGDGBD. The letters correspond to the pitch of each string from 6 to 1 respectively. This tuning gives you G major when strummed open.
G, C and D makes up the 1, 4 and 5 change pattern in this tuning. G is the open chord; C and D are located at the 5th and 7th fret respectively and the octave at the 12th fret.
The open G major tuning is great for slide guitars. Slides and riffs are elements you have to deal with in slide guitar blues. A common closing riff for the blues is the chromatic passing note from 4 to 5, which are C and D respectively on this tuning.
The shuffle pattern can be used in this tuning for creating your 12 bar blues. The shuffle pattern is basically a 5th and a major 6.
To start your 12 bar blues in open G major, apply the shuffle pattern on your 1, 4, 5 change. Do 4 bars on G, 4 bars on C and 4 bars on D to get a feel for the pattern. Once mastered, mix it up with a variety of riffs and slides. This adds a little spice in the rhythm you’re making. Try this variation for starts: 4 bar G, 2 bar C, 2 bars G, 1 bar D, 1 bar C, 2 bars G (shuffle pattern) and a closing riff.
12 Bar Blues in Open G major Tuning:
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