A fingernail glissando can be carried out from one up to three-four notes per hand. It is more percussive and can have a more energetic sound than a normal glissando.
It can be practiced in two different ways: either by leaving the hand in the “normal” position that would be used for a common glissando and attacking the strings with the nails, or by turning the hand and letting the back of the nails (the nails surface) slide on the strings. In first case, the posture of the fingers is a more round one, in second case the fingers are quite stretched.