These 12 bells, installed within the domed roof of University College London’s North Observatory, are variously made of porcelain, stoneware, or reclaimed terracotta.  Each bell contains a small speaker, which enables each bell to play back recordings of itself. These recordings were made

a) directly after the first firing or
b) after being glazed and refired.  
Each bell’s tone rose significantly (usually about 1 octave) following the second firing.  Therefore, some of the recorded sounds now echoing out of each bell are actually tones which the bell can never make again.

Additionally, some of the sounds have been made by digitally stretching the recorded sound of the bell – using an algorithm to make the note last longer, filling in the new pieces of time with old pieces of sound, as it were.

This composition for the bells is approximately 6 minutes and 51 seconds long; however, in its installation it loops continuously. Therefore, the piece’s duration is designated by the beginning and end of listening.