Cluster voicings are another possibility to add interesting harmonic structures to your music. As opposed to “normal” clusters that stack minor OR major seconds, cluster voicings follow a certain scale structure incorporating only notes of the current scale into the voicing. As a result a cluster voicing might consist of minor AND major seconds (and in rare cases augmented seconds).
Cluster voicings are formed out of adjacent scale notes, for example a lydian cluster voicing might consist of F#, G, A, B and C (usually with the root C reinforced to mark it as a tonal center). Still, as these voicings rely on a certain scale, they imply a tonality in spite of their very dense structure.
Such voicings work great when building towards a climax with lots of tension, e.g. writing a phrase that starts with open voicings that get increasingly dense towards the climax where it reaches a cluster voicing.
It also works to use cluster voicings in a whole passage, especially action drriven scores benefit highly from such voicings. Another technique that has its origin more in modern Big Band writing but nevertheless is very useful in orchestral writing as well is to harmonize a melody in cluster voicings (preferably doubling the melody line at unison or an octave to make sure it stands out on top of the dense structure). Generally, due to the thickness of these voicings, they need to be orchestrated with care to not result in a muddy wall of intransparent sounds.