The curved bow for string instruments enables string players to control the tension of the bow hairs in order to play one, two, three and four strings simultaneously and to change easily among these possibilities. The high arch of the bow allows full, sustained chords to be played and there is a lever mechanism that affects the tension and release of the bow hairs.
The practice of polyphonic playing is documented by Alessandro Striggio (1540–92), violinist Nicolaus Bruhns (1665–97), and German violinist Johann Paul von Westhoff (1656–1705), who also developed a unique notation for that. There exist also some polyphonic pieces for violin and viola by Niccolò Paganini (1782–1840), documented by Dr. Philippe Borer.[1]
Ever since the publication in 1905 of Albert Schweitzer's book about J. S. Bach,[2] the question of the curved bow has been widely debated. For Schweitzer, however, use of the curved bow was essential in performing Bach’s string works. Asked to write something for the Bach year in 1950 (Bach-Gedenkschrift), forty-five years after his original study, Schweitzer still focused on his ideas about the curved bow.[3]
Certain musicologists (D. Boyden, for example) have questioned the use of the curved bow, but their notions seem to be based more on theory than actual use of the bow itself. Two texts, on the other hand, clearly document use of the curved bow: Rudolf Gaehler’s book Der Rundbogen für Violine - ein Phantom? (The Curved Bow for Violin - a Phantom?),[4] and Michael Bach’s article on the Suites for Cello of J.S.Bach.[5]
In 1990, German cellist Michael Bach had invented a curved bow for cello, violin, viola and bass.[6] He named it "BACH.Bogen" (BACH.Bow). During the years 1997 and 2001, Mstislav Rostropovich was intimately involved in the development and testing of the BACH.Bogen.[7] He invited Michael Bach to present his curved bow on the occasion of the 7ème Concours de violoncelle Rostropovitch in Paris 2001.[8]
John Cage, Dieter Schnebel, Walter Zimmermann and Hans Zender have written works for the curved bow which explore the new perspectives and potential of it.