One technique that Eric Clapton relied on heavily was the use of the wah-wah pedal which mimicked the old blues sound employed by Robert Johnson of the slide guitar. Clapton credits much of his musical creation to ideas he drew upon from American blues artists and the wah-wah pedal was his main way of blurring the lines between rock and blues.
(https://www.youtube.com/watch?v=n9ODNQPQo3A)
As Clapton explains in this video, when he rocks his foot on the pedal, it takes the bass sound off and puts treble on. The wah-wah pedal creates clear treble sounds that gradually become muffled bass tones to create the unique “wah” sound, which drastically changes the timbre over the course of one note played on his guitar (Matthews 1997). This sound was also produced by Robert Johnson, but in a different way. He placed a tube slide over one of his fingers and literally slid his hand up and down the neck of the acoustic guitar to make the sound. The technological advancements of effect pedals, amplifiers, and distortion in the 1960s eliminated the need for Clapton to play his electric guitar this way and granted him the ability to play thicker-textured chords that give his songs their rock feel instead of just being the blues (Palmer, 2005).