I’ve been playing my cello everyday since November 9th and finger left finger tips are now finally callused enough that I don’t really notice the strings any more. My practice session are usually 30 to 45 minutes long, and my lessons are 40 minutes long. On lesson days I play close to 90 minutes as I practice at home after the lesson which doubles my playing time.
For the first couple of weeks my finger tips were sore, especially when playing. The soreness gradually faded and now I am not aware of any soreness or pain while playing. The two outer fingers, #1 (forefinger) and #4 (pinkie) don’t contact the fingerboard at a 90º angle. Imaging gripping a softball with your left hand and then bring your fingers down on to a flat surface. The forefinger is rolled slightly toward the thumb side, and the little finger is rolled slightly aware from the other fingers. Consequently the callus is on the outer edge of those fingers. The middle and ring finger, numbers 2 and 3, do contact the fingerboard perpendicularly, so their callus is centered on the tip of the finger.
My tone has steadily improved and I believe it’s largely due to the toughening of my finger tips. When playing an open string the vibrations are stopped by the bridge at one end and the nut at the other end. When stopping a string to change its pitch with a finger, anything less than completely stopping it against the fingerboard results in a less pure tone. When my fingers were still developing calluses it was harder (painful at times) to get a good stop and the tone reflected that.
The other factor that has improved my tone is better placement. I am getting better and better at “seeing” where my fingers are with my hearing. Playing the right note, and playing it with a properly stopped sting, vastly improves the tone and sound of the music.