Players of brass instruments with piston valves can smear a note by depressing the valves slightly, which broadens the "slot" allowing the player to portamento smoothly between two notes.
Is there a trombone counterpart of this technique?
One specific example - on a trumpet it's possible to half-valve smear an octave. You can't use the trombone slide to smear an entire octave. So how would you portamento an octave on trombone?