Air notes

Blowing air through the instrument without deliberately sounding a pitch. Notated with a verbal instruction. Pitched air notes are very quiet. Unpitched notes may be made louder by allowing air to escape around the mouthpiece. 'Half and half' (i.e. half an embouchure) is quite efffective in the low register of the bass clarinet.
Air notes (clarinet):
Air notes (bass clarinet):

Key Clicks

Rattling instrument keys. Notated with x-shaped notehads and a verbal instruction. Relatively quiet on clarinet, but quite effective in the low register of the bass.
Key clicks (clarinet):
Key clicks (bass clarinet):

Multiphonics (played)

Playing chords. In non-specific situations, notate by writing a bottom note with the word 'chord' above. Although specialist manuals often give highly detailed fingerings for chord production, the variability of production makes this generally a non-specific effect. However, instruments and players vary in the multiphonics they can find. For more specific notations, consult specialist manuals.
Multiphonics (clarinet):

Multiphonics (sung)

It is possible for voice and instrument to sing and play either the same or different notes, and for both to move independently of one another. Watch out for the vocal range!
Write the sung notes in small noteheads, plus a verbal instruction. Sung multiphonics (clarinet):



Intervals smaller than a semitone. Notations vary, but the examples above show a microtonal inflection and a quartertone. Produced by using 'fake' fingerings and/or adjusting the embouchure. Microtones on the clarinet are practicable, but obviously need a great deal of care and attention to detail. Consultation with the player is probably the best way forwards.
Microtones on the bass clarinet are much more problematic, because of the covered holes.

Microtones (clarinet):
Microtones (clarinet):

Alternative Fingerings

There is no need to specify fingerings normally, so the use of alternative fingerings is generally left to the player. There should be a very good reason for specifying alternative fingerings!
Alternative fingerings:

Without Mouthpiece

Removing the mouthpiece and blowing into barrel. Perfectly possible, but not particularly effective.
No mouthpiece:

Slap tongue

Best as a bass clarinet effect, comrpsing a violent release of the tongue, creating a 'slap' as the vacuum is opened. Notate with a verbal instruction.

Slap tongue (clarinet):