Mozart Never Played This Piano

Around 1700, in Florence, Bartolomeo Cristofori was keeper of instruments to Prince Ferdinando de' Medici. A court inventory of that year records a new instrument of his invention, shaped like a harpsichord, with hammers and dampers and a range of four octaves. In 1711 the writer Scipione Maffei described it as a gravicembalo col piano e forte, a harpsichord with soft and loud, and the end of that phrase is the name that survived.

The problem it solved is easy to hear. A harpsichord plucks its strings with quills, and a pluck is the same strength however hard you press the key. A player can change the registration or the number of strings sounding, but within a phrase cannot make one note louder than its neighbour. Cristofori replaced the pluck with a hammer thrown at the string, and the harder the key was struck, the harder the hammer hit.

The hard part was letting go. A hammer that stays against the string damps it at once. Cristofori's action threw the hammer at the string and then let it fall clear, a mechanism called the escapement, so the string could ring while the key was still held down. Every piano action since is a refinement of that idea. Three of his instruments survive, the oldest, from 1720, in the Metropolitan Museum in New York.

For the rest of the eighteenth century the new instrument stayed light: a wooden frame, thin strings, leather-covered hammers, a range of about five octaves. That is what Mozart played. His own, made by Anton Walter in Vienna in the early 1780s, is still in Salzburg. Its notes speak instantly and fade fast. Passages that blur on a modern grand are transparent on it, and the balance between the hands is different, because the bass is light rather than booming.

Then the instrument was industrialised, and the decisive material was iron.

String tension is what makes a piano loud and sustained. Heavier strings under higher tension carry more energy, but a wooden case can take only so much pull before it twists. Makers added iron bracing piece by piece, and in 1825 Alpheus Babcock in Boston patented a frame cast in a single piece. With iron taking the load, tension could rise far beyond what any wooden case could hold.

The action changed too. In 1821 Sébastien Érard's double escapement was patented, letting a note be struck again before the key had fully risen, so repeated notes could be played at speed. And in 1859 Steinway & Sons in New York patented an overstrung grand, its long bass strings running diagonally over the others so they could be longer and sit nearer the middle of the soundboard. An iron frame, crossed strings and a fast repeating action: by the 1860s the layout of the modern concert grand was essentially settled, and the keyboard had grown to about seven octaves.

Why did all this happen? Partly because it could: foundries, factories and cheap iron arrived. But mostly because of where music was being played. A fortepiano is a drawing-room instrument. The nineteenth century built public concert halls and filled them with paying audiences, and an instrument that had to reach the back of a hall full of people had to be a different machine.

Beethoven lived through the change, and you can hear it in his music. His early sonatas fit inside five octaves. His late ones use about an octave more, and their textures assume an instrument heavier and more sustained than the one he started on. He was writing for pianos that were changing under his hands.

So when a pianist plays Mozart on a modern Steinway, it is a kind of translation. The notes are the same; the instrument is not. Whether that betrays the music or gives it something it can carry is one of the standing arguments of performance, and it is worth knowing that it is an argument rather than a settled default. The name piano covers two centuries of very different machines, and Mozart never played the one you have most likely heard him on.