Scordatura Notation
Scordatura notation was first used in the late seventeenth century as a way to quickly read music for violin with altered tunings. It was a natural choice for viola d'amore and other stringed instruments not tuned in the usual fifths, especially those whose intervals between strings are not uniform across their range. Biber, Vivaldi and Vilsmayr (a student of Biber), among others, wrote pieces for violin with one or more strings retuned to notes other than the usual fifths. Given that the viola d’amore was usually played by violinists and that many different tunings were used, scordatura notation made it easier for a violinist to read the music.
Scordatura notation exists in a number of different types. Treble clef, alto clef and soprano clefs are all used by different composers. Bass clef is typically used for notes on the lower two or three strings (6 or 7 string instruments) and usually sounds an octave higher than written. In scordatura, one imagines that one is playing a violin (or in some cases a viola, where alto clef is used) tuned in the normal fifths. Scordatura notation informs the player not about what note will sound but rather about where s/he should place his/her fingers; therefore, it may be referred to as a tablature or "finger" notation.
In Biber’s Harmonia Artificiosa no. VII, a different version of scordatura notation is used. Biber uses a nine line staff. The clefs used are based on alto clef (imagining that you are playing a viola). The piece is written for a six stringed instrument. The upper part of the staff supposes that you are playing on the upper four strings and the lower part that you are playing on the lower four strings (still imagining that you are reading the four strings of a viola in alto clef). This does mean that there are two ways of notating notes on the middle two strings but it quickly becomes apparent, when playing, what the correct reading should be.
Read more about this topic: Viola D'amore