Stringjoy Naturals 10-24 Phosphor Bronze Wound 12-strings Extra Light acoustic guitar string set. Naturals are Stringjoy take on Phosphor Bronze, which is great at bringing out the the authentic, woody characteristics of an acoustic guitar. It is this rich copper alloy that gives these strings a distinctly warm, resonant tone. The strings also have a rose gold color so beautiful you will want to order an extra set just to frame and hang on the wall.