key

…to the white and black keys on the modern piano) was only gradually standardized. The arrangement of the keys depended in part on the music played and partly on the current state of musical theory. Thus, early keyboards are reported with only a single raised key in each octave (B♭),…

…the white tops of piano keys (“ivories”) and white billiard balls, were replaced by equivalents made of plastics or other synthetic materials. See also ivory carving.