You may have noticed an unusual sound at the end of the turnaround in the previous exercise. It was using an Augmented chord (indicated by the symbol +), which was used extensively by T-Bone Walker.
The degrees of the Augmented chord are 1 3 and #5. Another unusual sounding chord featured in some Blues songs is the Diminished 7th chord (indicated by the symbol o). Its degrees are 1 b3 b5 and bb7 (=6) . The following diagrams show the most common fingerings for these two chords. For more information about these types of chords, see Progressive Complete Learn to Play Guitar Chords Manual.
This new 12 Bar Blues first makes use of the diminished chord in bar two. It also uses the augmented chord in the turnaround.