The history and development of modern pianos is indelibly tied to advances in metallurgy.
Innovations in the production of piano strings, in particular, fundamentally changed pianos between the late 18th century and mid-19th century, allowing the tonal range of the instruments to increase from 5 to 7 1/3 octaves.
With limited options available to manufacturers, wires in early pianos were made exclusively from iron.
But following Bessamer's advances in steel-making, more ductile and corrosion resistant steels quickly came to replace crude iron strings. Shortly thereafter a stainless steel high in chromium and nickel was developed.
Carbon steel wires like ASTM A227 continue to be the most commonly used wires for all sections of modern pianos. However, wires in the bass section are often formed with copper and nickel wrappings, which are used to improve the richness and harmonic quality of the sound.
Gauges of wire can range from 0.006 inches to 0.192 inches (0.15 to 4.8 mm).
Image: Stainless steel piano wires. Author: Matt Billings. Courtesy Wikipedia. Licensing: Creative Commons Attribution 2.0 Generic