When a string player refers to an ‘open string’ it means that one of the four strings is being played without the left hand fingers being involved or touching the string. The word ‘open’ is appropriate as the sound the strings make is highly resonant and pure in sonority. Pieces of music based on scales or arpeggios that derive from open strings have a powerful, projecting quality that allows the stringed instrument to resonate freely. It’s no coincidence that many of the famous violin concertos have been written in the keys of an open string (G, D, A and E on a violin), for example the Beethoven and Brahms Concertos in D major or the Mendelssohn Concerto in E minor. Bach wrote violin concerto’s in E and A minor and Mozart’s three most famous violin concertos were written in G, D and A major. One notable exception of a great Concerto that is not written in an open string key is Elgar’s Concerto in B minor but this is still a very strong key on the violin with an open D string present in a B minor scale. It could be said that this work has a more complex key character which Elgar would have chosen for a reason.
Boccherini (who was himself an accomplished cellist) used the keys of the open strings of C, D, G and A on the cello in several of his cello Concertos, however two very celebrated Concertos for cello are written in less likely keys with the Dvorak Concerto being in B minor and Elgar writing in E minor. Elgar’s choice of key is interesting because it relates to his choice of key for the violin Concerto (both being a fifth above the highest open string of the respective instruments). The Dvorak Cello Concerto is a bit puzzling because B minor may not project as well on a cello as say G major but then a B minor arpeggio also can include an open D string.
Open strings on a viola are C, G, D and A (being an octave above the cello) and Concertos for this instrument include works by Bartok, Hindemith, Walton, Telemann, Stamitz and Rolla. Telemann, Walton, Stamitz and Rolla followed the norm of writing for open stringed keys and made the best use of the wonderfully resonant sound of the viola.
In a string arrangement or composition for string orchestra, the use of open strings can have a striking effect as the simultaneous ringing of several open strings generates a marvellously full and resounding note. When a composer sits down with the aim of writing a work for string ensemble or solo stringed instrument, by harnessing the qualities of an open stringed key this can help the piece to be comfortable to play and utilise the benefits of open strings to the utmost.