Pure Nickel wound strings were used exclusively on most guitars built in the Fifties and most of the Sixties. Pure Nickel has a slightly warmer tone than nickel-plated steel and is preferred by many blues artists. Pure Nickel Wound strings are created by wrapping Pure Nickel alloys around a hex-shaped core wire which is made from tin-plated high-carbon steel (same as plain strings, but hex-shaped).