structural:expansion, stylistic:tone, linguistic:translation
Harmonics

Lightly touching the string with a fingertip at a harmonic node, but without fully pressing the string, and then plucking or bowing the string, creates harmonics. Instead of the normal tone, a higher pitched note sounds. Each node is at an integer division of the string, for example half-way or one-third along the length of the string. A responsive instrument will sound numerous possible harmonic nodes along the length of the string. Harmonics are marked in music either with a little circle above the note that determines the pitch of the harmonic, or by diamond-shaped note heads. There are two types of harmonics: natural harmonics and artificial harmonics (also known as false harmonics).

Natural harmonics are played on an open string. The pitch of the open string when it is plucked or bowed is called the fundamental frequency. Harmonics are also called overtones or partials. They occur at whole-number multiples of the fundamental, which is called the first harmonic. The second harmonic is the first overtone (the octave above the open string), the third harmonic is the second overtone, and so on. The second harmonic is in the middle of the string and sounds an octave higher than the string's pitch. The third harmonic breaks the string into thirds and sounds an octave and a fifth above the fundamental, and the fourth harmonic breaks the string into quarters sounding two octaves above the first. The sound of the second harmonic is the clearest of them all, because it is a common node with all the succeeding even-numbered harmonics (4th, 6th, etc.). The third and succeeding odd-numbered harmonics are harder to play because they break the string into an odd number of vibrating parts and do not share as many nodes with other harmonics.

Artificial harmonics are more difficult to produce than natural harmonics, as they involve both stopping the string and playing a harmonic on the stopped note. Using the octave frame (the normal distance between the first and fourth fingers in any given position) with the fourth finger just touching the string a fourth higher than the stopped note produces the fourth harmonic, two octaves above the stopped note. Finger placement and pressure, as well as bow speed, pressure, and sounding point are all essential in getting the desired harmonic to sound. And to add to the challenge, in passages with different notes played as false harmonics, the distance between stopping finger and harmonic finger must constantly change, since the spacing between notes changes along the length of the string.

The harmonic finger can also touch at a major third above the pressed note (the fifth harmonic), or a fifth higher (a third harmonic). These harmonics are less commonly used; in the case of the major third, both the stopped note and touched note must be played slightly sharp otherwise the harmonic does not speak as readily. In the case of the fifth, the stretch is greater than is comfortable for many violinists. In the general repertoire fractions smaller than a sixth are not used. However, divisions up to an eighth are sometimes used and, given a good instrument and a skilled player, divisions as small as a twelfth are possible. There are a few books dedicated solely to the study of violin harmonics. Two comprehensive works are Henryk Heller's seven-volume Theory of Harmonics, published by Simrock in 1928, and Michelangelo Abbado's five-volume Tecnica dei suoni armonici published by Ricordi in 1934.

Elaborate passages in artificial harmonics can be found in virtuoso violin literature, especially of the 19th and early 20th centuries. Two notable examples of this are an entire section of Vittorio Monti 's Csárdás and a passage towards the middle of the third movement of Pyotr Ilyich Tchaikovsky's Violin Concerto. A section of the third movement of Paganini's Violin Concerto No. 1 consists of double-stopped thirds in harmonics.

When strings are worn, dirty and old, the harmonics may no longer be accurate in pitch. For this reason, violinists change their strings regularly.