https://courses.lumenlearning.com/vccs-tcc-mus121-1/wp-admin/post.php?post=759&action=edit

The concept of a prepared piano is a fairly simple one, but the range of tonal possibilities a prepared piano can produce is nearly infinite.

Introduction

A prepared piano is a piano that has had its sound altered by placing objects (called preparations) on or between the strings.

John Cage

The invention of the “prepared piano,” per se, is usually traced to John Cage. Cage first prepared a piano when he was commissioned to write music for “Bacchanale,” a dance by Syvilla Fort in 1938. For some time previously, Cage had been writing exclusively for a percussion ensemble, but the hall where Fort’s dance was to be staged had no room for a percussion group. The only instrument available was a single grand piano. After some consideration, Cage said that he realized it was possible “to place in the hands of a single pianist the equivalent of an entire percussion orchestra. . . . With just one musician, you can really do an unlimited number of things on the inside of the piano if you have at your disposal an exploded keyboard.”