Classic electric guitar string tone dates back to the 1950s, when pure nickel was the primary alloy used. As the need for brighter tone and higher magnetic electric guitar strings grew in the '60s, nickel-plated steel became the industry standard. D'Addario's EPN120 XL strings feature nickel-plated steel, but these XL Pure Nickel strings offer a warmer, vintage tone alternative which many enthusiasts prefer.