Portamento
A gliding transition between two notes, above all with voice and strings.
What it means
Portamento designates a gliding transition from one note to the next: the pitch is not leapt but led through the space between. With singers this happens with the voice, with string players by sliding the finger on the string, with trombones through the slide.
Portamento is to be distinguished from the glissando. In the glissando, the notes lying in between are audibly executed — on the harp or piano as a scale, on string instruments as a distinct running-through. Portamento, by contrast, connects two notes without emphasizing the intermediate steps; it is a means of expression, not a figure. The boundary, however, is fluid, and the terms are not used the same way everywhere.
It is also not to be confused with portato, which designates a quite different articulation.
In the notation
Portamento is usually indicated by a straight or slightly wavy line between the two noteheads, occasionally additionally by the word. In vocal and string parts it also stands encoded as a fingering indication, when two notes are to be played deliberately with the same finger. In many cases it is not notated at all but part of performance practice.
Musical use
Portamento belongs among the expressive means of song-like playing. It is widespread in vocal music and in the string literature of the nineteenth century; the extent of its use has decreased noticeably over the course of the twentieth century. It is used with large interval leaps and at passages of particular intensity, where the connection of the notes is to become audible.
In the nineteenth century, portamento was very widespread among string players and singers; today it is used more sparingly.
Performance practice
Use the device sparingly; used often it loses its effect and sounds sentimental. Execute the glide briskly and do not let it take up the whole note duration — the goal note should be reached in time. Take care that the volume does not increase during the glide. And check the style: in music before the nineteenth century, restraint is appropriate.