Chapter 26 tells of preparing an older Steinway piano for a concert. Here is a LINK to a very good video for observing how a grand piano action works. In the video, the various parts are isolated, and then the entire action is shown moving. At that time, you can observe the pivot point of the hammer shank. It appeared as just a hole in the wood when the hammer was isolated. That hole is lined with a red cloth bushing which is reamed to a specific setting so that there is a specific slight resistance to movement when a metal pin is inserted. That pin is known as a “center pin” and acts like a hinge pin for the movement of the hammer shank.
You may recall that older Steinway pianos had the wooden parts dipped in a liquid paraffin which wicked down into the red cloth bushings. The paraffin would react with the nickel of the pin, creating a green substance that gums up the bushing, restricting movement. The story in Chapter 26 told of reaming out each of 88 hammer action centers, in order to remove the verdigris, the green substance which was gumming up the hammer shank action centers. This would be only a temporary fix, as the paraffin was impregnated into the wood of the hammer shanks, and it continued to wick down into the bushings.
Here is a LINK for an analysis of how difficult it is to play the Liszt B-minor Sonata. Included in the article are opportunities to hear the different themes of the work. Here is a LINK to hear a spectacular performance which has the printed music on the screen, so you can read it as the sonata is played. At about 7:30 minutes in, you may notice a number of delicate passages and trills that require perfect regulation of the hammer action centers. You can imagine how impossible the piece would have been to play before the piano was repaired.
I hope you enjoyed the recording.