The most common use of finger crossing is in scale playing. This technique allows a quick way to change position. When playing scales, the thumb is placed under the third or the fourth finger in the right hand (ascending) and the left hand (descending). On the descending scale, the third and the fourth finger is placed over the thumb in the right hand, and on the ascending scale – in the left hand.
Note, that we must also make use finger preparation in this technique as well. This means that we must place the crossing finger to the next position in advance. It will prevent your fingers from hitting the wrong keys. Relax your fingers and make them slightly curved. Remember to keep all fingers in contact with the keyboard at all times and play with as little excess energy as possible.
Another instance of finger crossing is when playing two notes in one hand. At first, try finger crossing when one note is held and another is moving. Note the general rule of thumb here: place the longer finger over the shorter one and place the shorter finger under the longer one.
Try this use of finger crossing in the following exercise:
1) Play a note C with the thumb of your right hand.
2) While holding this C, play an ascending scale using fingers 2, 3, 4, and 5 of the same hand.
3) As you reach G with your fifth finger, place the fourth finger over the fifth and play A.
4) Then play B with your fifth finger.
5) Repeat the steps 1 through 4 playing the descending scale in the left hand.
6) Now play a note C with the fifth finger of your right hand.
7) While holding this C, play a descending scale using fingers 4, 3, 2, and 1 of the same hand.
8) As you reach F with your thumb, place the second finger over the thumb and play E.
9) Then play D with the thumb again.
10) Repeat the steps 6 through 9 playing the ascending scale in the left hand.
11) Repeat the entire exercise starting on D, E, F, G, A, and B.
Play slowly using just one hand at a time. After some time, when it will become comfortable, you can practice this exercise with both hands together.
Finger crossing is especially useful for playing scales in parallel intervals using one hand in difficult music, most often the thirds (and the sixths, if you are technically advanced).
Then you would need to hold one note with the fifth finger in the right hand (ascending) or the left hand (descending). As you hold this note, lift your third finger and place it over the fifth finger to the next note. That way the top note will be played legato.
When playing an ascending scale with the left hand, hold your thumb. The same applies for the descending scale using the right hand. As you hold the note with your thumb, lift your third finger and place it over the thumb to the next note. Again, playing this way will ensure a smooth legato of the top voice.
Try this exercise on C major scale. First practice it over one octave, later move to two octaves, and finally, play it over four octaves. Play very slowly using just one hand at a time. After some time, when it will become comfortable, you can practice playing the C major scale in double thirds with both hands together. This exercise will develop your finger independence as well.
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