Upright Piano by Heintzman

The prominent Toronto, Canada firm of Heintzman & Co was one of a few that made pianos with transposing keyboards. The most famous user of a transposing keyboard was Irving Berlin, who learned to play by ear, and favored the black keys, playing mostly in F sharp major. Making an action that allows for transposition is challenging, as the keys need to move under the action. The gaps caused by plate struts need to be evened out, and Heintzmann did this by using metal “stickers” descending from the wippens, which were bent to produce an even spacing of all notes. On the positive side, the keys could all be perfectly straight.

Credit: Piano Technician's Guild