A series of useful and expressive techniques for use in many various styles of composition.
Quartertones and Microtones
Intervals smaller than a semitone. Notation methods vary, but these examples are typical of quartertones and raised & lowered inflections. Quartertones and microtones are produced by using 'fake' fingerings and/or by adjusting the embouchure.
Playing chords - more than one note at a time. Write the bottom note of the chord and the word 'chord' above. Occasionally composers write all the notes of the chord that they wish to hear and/or provide a fingering diagram. There are many possible multiphonics on both oboe and cor anglais however instruments and players vary in the multiphonics they can find.
Rattling instrument keys. Notated by x-shaped noteheads and verbal instruction. This effect is not particularly loud.
Blowing air through the instrument without deliberately sounding a pitch. Written with verbal instruction in the music. This technique is very quiet!
Sustaining a note whilst breathing in through the nose. Another technique that as notated by verbal instruction in the music. Although this is easier on double reed instruments than most others, it should be regarded as an unusual technique and players should be consulted before it is used!