Piano extended techniques
He even used special notation for certain of them: "hold keys silently" is indicated by square note heads rather than the usual round ones.Karlheinz Stockhausen took these ideas further in his series of works entitled Klavierstücke in which the pianist is often instructed to wear protective gloves while playing cluster glissandi with the hands.Sofia Gubaidulina, in her Sonata, instructs the pianist to use nontraditional sounds: sounds produced by a glissando performed with a bamboo stick on the piano pegs against a cluster performed on the keyboard; a "buzzing" sound created by placing the bamboo stick on vibrating strings; pizzicato effects produced by plucking the strings; glissando effects produced by rubbing along the strings using a fingernail; and a muted effect produced by touching the strings.Composers also instruct the pianist to partially damp strings with the finger tips to create harmonics (e.g. George Crumb, Eleven Echoes of Autumn, Eco I).Another technique involves the physical "preparation" of the piano using foreign objects inserted between the strings or attached to the hammers.