Does it make any difference if my fingers are held very much curved or only a little? I was told that Rubenstein used his fingers almost flat.
Since you mention Rubinstein I may quote his saying: "Play with your nose, if you will, but produce euphony (Wohlklang) and I will recognize you as a master of your instrument." It is ever a question of the result, whether you play this way or that way. If you should play with very much curved fingers and the result should sound uneven and pieced, change the curving little by little until you find out what degree of curvature suits your hand best. Experiment for yourself. Generally speaking, I recommend a free and easy position of hand and fingers, for it is only in a position of greatest freedom that their elasticity can be preserved, and elasticity is the chief point. By a free and easy position I mean that natural position of hand and fingers into which they fall when you drop your hand somewhat leisurely upon the keyboard.
Cantabile Passages
Should a cantabile passage be played with a high finger-stroke or by using the weight of the arm?
Certain characteristic moments in some pieces require the high finger-stroke. It may be used also in working up a climax, in which case the raising of the fingers should increase proportionately to the rise of the climax. Where, however, the strength of the fingers is sufficient to obtain the climacteric result by pressure, instead of the stroke, it is always preferable to use pressure. As a general principle, I believe in the free-hanging, limp arm and recommend using its weight in cantabile playing.
An Incorrect Position of the Fingers
Pray how can I correct the fault of bending out the first joints of the fingers when their cushions are pressed down upon the keys?
Your trouble comes under the head of faulty touch, which nothing will correct but the constant supervision by a good teacher, assisted by a strong exertion of your own will power and strictest attention whenever you play. This bending out of the first joint is one of the hardest pianistic ailments to cure, but it is curable. Do not be discouraged if the cure is slow. The habit of years cannot be thrown off in a day.
[5. ACTION OF THE WRIST]
Don't Stiffen the Hands in Playing Scales