GP Halls CD 'Embarkation' has been slightly delayed due to problems with printing. Just to wet your appetite here is a photo of GP from the 70s with the pianos he used to record his Estates album.
This is what he says about them:
There were 2 piano frames used, one was a percussion piano frame the other a solo piano frame. one was single and the other was double (meaning another frame bolted on-to the top of the wooden base so air/harp type sounds could be accomplished, each were tune in banks of chords, the tunings have been lost, and I have no idea now what they were, the percussive use of metal chains dragged over the chords and slammed down caused an explosive tuned sound energy, also on top of this air sounds were used as the dying crescendo faded ( this frame had no wooden structure supporting it ) anything that enhanced the sound chords were used. The Estates had movements and melodic themes + avant garde improvised sections
These piano frames were made by myself in 1970 and were the first Industrial Sound-Sculptures a genera I invented. I used them also with a mobile theatre company touring Europe, called "engineers of the imagination" (Welfare State) based at the time in Burnley Lancashire, and were last seen being burnt in a fire sculpture installation somewhere.