Martin Phosphor Bronze strings are made from 92/8 composition to give that brilliance, clarity, and longevity of sound required by serious guitarists. The Phosphor Bronze winding alloy is ideally suited for making strings that have deep, rich basses and clear, bright trebles. Martin Strings are high quality strings for daily use. Core and wrap wires must meet strict requirements in order to make the grade. Martin Strings are wound to precise specifications.