Scordatura
A retuning of the strings.
What it means
Scordatura means tuning one or more strings differently from usual. Instead of the violin's customary fifths, for instance, the lowest string can be raised by a whole tone or the highest tuned down. This shifts the whole fingering system: the player continues to stop the strings in the accustomed pattern, but something different sounds. This is why scordatura is often notated in fingering-tablature logic — one writes what is to be stopped, not what sounds.
In the notation
At the beginning of the movement, the required string pitches stand as a rhythm-less group of notes. Then follows an indication of whether the notation is for fingering or for sounding pitch; with fingering notation, the written image and the sound do not match, which is unfamiliar when reading. The return to normal tuning demands the marking accordatura.
Musical use
Retuning is done for three reasons: to make possible double stops and chords otherwise unplayable, to strengthen the resonance of a particular key, and to change the tone colour, since a string tuned up or down responds differently. The technique has its heyday in the seventeenth and early eighteenth centuries but is also used afterward, for instance when a solo violin is to sound especially cutting or an instrument is to sound foreign. It is also widespread in folk-music traditions of various regions.
Performance practice
Reckon with a retuned string holding its tuning only after a few minutes; retune early, therefore, and check shortly before the entrance. Too much raising strains the string, the bridge, and the top — keep to the prescribed pitch and, if necessary, use a string suited to it. When reading fingering notation, it helps to write the sounding version alongside once, to check the intonation within the ensemble. If retuning is not possible in concert, a second, already retuned instrument is the usual solution.
Bear in mind that the changed tension affects the sound of the whole instrument: a string tuned down responds more sluggishly and sounds duller, one tuned up brighter and more tense. Reckon with this when shaping and adjust the bowing. Check whether the prescribed tuning is achievable with your strings, and use suitable strings if necessary. Check again shortly before the entrance, because retuned strings give way for a long time.