So in various sections of a piece I want the pianist to lift the pedal slower than usual, achieving an interesting effects as the harmonics fade. In some areas the pedal lift might be slower or faster, and so it would seem that just writing 'lift slowly' won't be effective. For this reason I'm wandering if there might be a graphic solution for notating pedal lifting, such as using hairpins?
You can make a remark at the beginning of the piece (perhaps write a foreword). Make a legend for the individual pedal stages and describe what sound the player should achieve.
*use pedal slightly. Allow strings to vibrate w/harmonics only.
Modern composers are very strict sometimes in giving detailed notes regarding the performing of their(!) musical intentions in the piece. Do the same.