Damped/muted glissando.

Muted glissando is a glissando that is muted at the same time as it is played.

Production

One hand plays a normal glissando while the other hand mutes the strings with the palm of the hand. In order to make a long muted glissando the muting hand must slide along the strings, following the playing finger.

Muted glissando.

Sound

The resonance of the harp's strings is damped thus the glissando sounds muted. 

Notation

A damping sign is added above or below the glissando.

Range

The whole harp.