D'Addario XL Pure Nickel strings look back to the '50s, when nickel was the primary alloy found in electric guitar strings. Into the '60s, these pure nickel strings would be supplanted when guitarists required brighter tone and enhanced magnetic properties/characteristic of the D'Addario XL nickel-plated steel string line, Pure nickel delivers classic, warmer timbres that define many genres including blues, classic rock, rockabilly, and more.