From Wikipedia: "John Cage was undoubtedly the composer who put the "prepared piano" concept on the world map, and coined the term. He credited Henry Cowell, and, to a lesser extent, Erik Satie, for contributing to the idea, and was probably unaware of many other precedents described below. Erik Satie prepared the piano for the performance of 'Le Piège de Méduse' (1913), a lyrical comedy considered to be the first example of surrealist drama. For its performance Satie put paper between the strings of the piano to create a mechanical effect."
We rediscovered the technique in complete ignorance of the precedents. I can't remember exactly what Gerard and I shoved into the piano frame. I think plastic rulers, protractors and lot of other pencil-case paraphernalia featured a great deal. (Ben)
Cutlery also, I think - and I think also some... ?bamboo sticks, ?like barbeque skewers. I may be hallucinating. (Gerard)