The selection of the fingers for the execution of a mordent depends always upon the preceding notes or keys which lead up to it. Since we cannot lift the hand just before a mordent for the purpose of changing fingers (for this would mean a rude interruption) we have to use whatever fingers happen to be "on hand." An exchange of fingers in a mordent is seldom of any advantage, for it hampers precision and evenness, since, after all, each finger has its own tone-characteristics.
[16. THE GLISSANDO]
To Play a Glissando Passage
Will you describe the best method of holding the hand when playing glissando? Which is preferable to use, the thumb or the forefinger?
In playing glissando in the right hand use the index finger when going upward, the thumb when going downward. In the left hand—where it hardly ever occurs—use the middle finger in either direction, or, if you should find it easier, the index finger downward. The production of so great a volume of tone, as is possible on our modern piano, has necessitated a deeper fall of the keys than former pianos possessed, and this deeper dip has banished the glissando almost entirely from modern piano literature.
[17. OCTAVES]
How Best to Play the Octaves
Should I play octaves using the "hinge" stroke from the wrist or by using the arm? I find I can get more tone by using the arm stroke, but cannot play so rapidly.
The character of the octaves must govern the selection of means to produce them. For light octaves use the wrist, for heavier ones draw more upon the arm. Rapidity requires that you avoid fatigue. If you feel fatigue approaching from too constant use of one joint, change to the other, and in doing this change also the position of the hand from high to low, and vice versa. For wrist octaves I recommend the low position of the hand, for arm octaves the high one.
Rapid Octaves