The minor blues scale, usually referred to as simply "the blues scale," is where the iconic sound of blues solo guitar comes from. The scale is almost identical to the minor pentatonic scale with a flat 5th scale degree added. The scale has six notes made up of the 1st, 3rd, 4th, flat 5th, 5th, and 7th scale degrees. The flat five creates a chromatic feel in the scale with three half steps in a row: the 4th, flat 5th, and 5th. This give the blues scale scale that unique sound which is rooted in the blues. Is also commonly used in rock, jazz, funk and other genres.
If you know how to play the minor pentatonic scales you can easily teach yourself the blues scales, especially if you know where the 4th and 5th notes are in each fingering position. To play the blues scales pictured below, play the minor pentatonic fingering while adding the blues note (the flat 5th) after each 4th.
The blues scales, like the pentatonic scales, can also be played diagonally or horizontally on groups of strings.