Chromaticism is a compositional technique interspersing the primary diatonic pitches and chords with other pitches of the chromatic scale. Chromaticism is in contrast or addition to tonality or diatonicism (the major and minor scales). Chromatic elements are considered, "elaborations of or substitutions for diatonic scale members."
Chromaticism is almost by definition an alteration of, an interpolation in or deviation from this basic diatonic organization.
Development of chromaticism 
As tonality began to expand during the last half of the nineteenth century, with new combinations of chords, keys and harmonies being tried, the chromatic scale and chromaticism became more widely used, especially in the works of Richard Wagner, such as the opera 'Tristan und Isolde'. Increased chromaticism is often cited as one of the main causes or signs of the "break down" of tonality, in the form of increased importance or use of:
- mode mixture
- leading tones
- tonicization of each chromatic step and other secondary key areas
- modulatory space
- hierarchical organizations of the chromatic set such as George Perle's
- the use of non-tonal chords as tonic "keys"/"scales"/"areas" such as the Tristan chord.
As tonal harmony continued to widen and even break down, the chromatic scale became the basis of modern music written using the twelve tone technique, a tone row being a specific ordering or series of the chromatic scale, and later serialism. Though these styles/methods continue to (re)incorporate tonality or tonal elements, often the trends which led to these methods were abandoned, such as modulation.
Types of chromaticism 
List of chromatic chords:
- Dominant seventh chords of subsidiary keys, used to create modulations to those keys (V7-I cadences).
- Augmented sixth chords
- Neapolitan sixth chords as chromatic subdominants.
- Diminished seventh chords as chromatic VII7
- Altered chords
- Expanded chords
- Shir-Cliff, etc. (1965).
Other types of chromaticity:
- Pitch axis theory
- Parallel Scales
- Nonchord tone
- The minor mode in major keys (mode mixture)
- Shir-Cliff, etc. (1965).
Chromatic note 
A chromatic note is one which does not belong to the scale of the key prevailing at the time. Similarly, a chromatic chord is one which includes one or more such notes.
A chromatic scale is one which proceeds entirely by semitones, so dividing the octave into twelve equal steps of one semitone each.
Linear chromaticism, is used in jazz: "All improvised lines...will include non-harmonic, chromatic notes." Similar to in the bebop scale this may be the result of metric issues, or simply the desire to use a portion of the chromatic scale
Chromatic chord 
A chromatic chord is a musical chord that includes at least one note not belonging in the diatonic scale associated with the prevailing key. In other words, at least one note of the chord is chromatically altered. Any chord that is not chromatic is a diatonic chord.
For example, in the key of C major, the following chords (all diatonic) are naturally built on each degree of the scale:
- I = C major triad [contains notes C E G]
- ii = D minor triad [contains D F A]
- iii = E minor triad [contains E G B]
- IV = F major triad [contains F A C]
- V = G major triad [contains G B D]
- vi = A minor triad [contains A C E]
- vii = B diminished triad [contains B D F]
However, a number of other chords may also be built on the degrees of the scale, and some of these are chromatic. Examples:
- ♭II in first inversion is called the Neapolitan sixth chord. For example in C Major: F-A♭-D♭. The Neapolitan Sixth chord resolves to the V.
- The ♯IV diminished chord is the Sharpened subdominant with diminished seventh chord. For example: F♯-A-C-E♭. The ♯IV diminished chord resolves to the V. The ♯IV can also be understood as the tonicization of V where it functions viio7 of the V chord, written viio7/V.
- ♭VI: The Augmented sixth chord chords resolve to the V.
Chromatic line 
Chromaticism is often associated with dissonance.
Susan McClary (1991) argues that chromaticism in operatic and sonata form narratives can often be understood as the "Other", racial, sexual, class or otherwise, to diatonicism's "male" self, whether through modulation, as to the secondary key area, or other means. For instance, Catherine Clément calls the chromaticism in Wagner's Isolde "feminine stink". However, McClary also points out that the same techniques used in opera to represent madness in women were historically highly prized in avante-garde instrumental music, "In the nineteenth-century symphony, Salome's chromatic daring is what distinguishes truly serious composition of the vanguard from mere cliché-ridden hack work." (p. 101)
See also 
- 20th century music - Classical
- Matthew Brown; Schenker (1986). "The Diatonic and the Chromatic in Schenker's "Theory of Harmonic Relations", p.1, Journal of Music Theory, Vol. 30, No. 1. (Spring, 1986), pp. 1-33.
- Cope, David (1997). Techniques of the Contemporary Composer, p.15. New York, New York: Schirmer Books. ISBN 0-02-864737-8.
- Shir-Cliff, etc. (1965). Chromatic Harmony. New York: The Free Press. ISBN 0-02-928630-1.
- Coker, Jerry (1997). Elements of the Jazz Language for the Developing Improvisor, p.81. ISBN 1-57623-875-X.
- Opera, 55-58, from McClary (1991) p.185n
- "Passus duriusculus", Bach-Cantatas.com.