It is interesting, long ago I had a few lessons with Lhevinne's student Yali Wagman, who told exactly the same thing about pinkie. Ironically, he himself was incredibly stiff and by that time already could not really play, let alone demonstrate.
Personally, besides of pinkie (as you rightly mentioned as the weakest and "hard to relax"), I believe in importance of thumb. Those two work as an enclosing "frame" for the hand. Since the thumb "looks" different direction and designed rather for a grip, it is the trickiest one to feel "like others".
Hi Marik, I agree with you entirely and consider the thumb and 5th finger the "pillars" of the hand. Regarding the thumb, I would be interested to know if your formative training (Moscow or elsewhere?) includes any similarities to that which I learned from the J. Lhevinne student that I studied with during HS and college (my formative training). I was taught to NOT move the thumb "as a finger," but rather (this is a bit difficult to describe) to lean upon it with the hand where the thumb resists relative upward colapse. I was told to think of the thumb "as a branch off a trunk." When I play Albert-bass pattern, my thumb does not come off of the key top. Instead my hand uses it as an axis of rotation where when I lift the lateral aspect of the hand it causes the thumb to sink into the key (the hand leans upon the thumb), and when I play the finger, the weight on the thumb is reduced causing the thumb key to rise back up. Anything like that in your training? I'm sure Lhevinne didn't invent this but rather learned it from Safanov (who didn't allow anyone else to teach Joseph when he was in the Lower School of the conservatory, thereby preparing him himself for his Upper Training). A few other features that I learned was to maintain the arches of the hand (longitudinally from finger-tip to wrist with elevated knuckles inbetween, and laterally from the thumb to the 5th finger (but with wrist lower than the knuckles). A peculiar trait that I was made to make natural, was the flexion of the 2nd finger (index) under
the hand when not used in chords and when playing octaves. This was done to prevent colapse of the hand (like a "magic tent pole"). Your hand will NEVER colapse if the 2nd finger is folded under. A close appoximation of what I'm talking about can be seen in the photograph titled, "Mr Lhevinne at the Keyboard," included in his little book, Basic Principles in Pianoforte Playing
(however it seems to me that in the picture he is just actually lifting after finishing a phrase with his thumb).
Since at this point my whole approach to the keyboard, fingers, technique, and tone production is rather a system, it is very hard to say what was exact influence. My musical education and schooling was quite eclectic. I started with my father, who was a student of one of the favorite Goldenweiser's students. In Moscow I mainly studied with my dear teacher Lev Naumov, who for many years was one of the most favorite Neihaus' assistants. He did not have any systematic approach to technique, other than complete relaxation coupled with artistic imagination.
On the other hand, in Moscow it was customary to sit in other teachers classes and observe all the "secrets" (so the lessons always were full of people). Besides, I played for almost all of them.
After that I was very much influenced by Pnina Saltsman--eminent Israeli pianist, who was Cortot student for many years since she was a little girl--with whom I was taking many lessons for some 5 years. For her all the sound (and everything) was in incredibly flexible wrist and very "grounded" sinking into the key. She used quite a bit what you are writing about "2nd finger to prevent collapse", but very often her 3rd joint would get broken (like famous picture of Rachmaninov at the keyboard).
Again, it is hard to say how throughout those years my concept of the thumb has developed and what was exact influence. Moreover, the thumb technique very much depends on every particular place, technical difficulty, or music context. But here is my feelings about the general principle of thumb work:
The thumb consist of 3 joints (not two, as many people think of it), where the last, 3rd one is "inside" the hand, close to the wrist. That's where its motion starts. It should be very fast and flexible, esp. with passage work, or arpeggio, when the cross over done mostly not with the turn of the hand, but the thumb reaching the next position, while the hand remains absolutely relaxed and calm, and arm assists with only the very last bit of inevitable pivot. It is very hard to explain or put into the words... maybe a little clip made with iPhone will help. Is it possible to download the file directly to the forum?
I think, I understand what you mean by "leaning". I use it a lot, esp. in thicker music sonorities (like Brahms, Rachmaninov), when the thumb almost rubs deep into the key. At those moments I like to "break" my 3rd joints--then it will never sound harsh.
The work on Alberti bass I actually divide into two steps. The first, work on it with fingers only (again, with absolutely calm and relaxed hand), and then add rotation. Unlike you, I feel the rotation around the 3rd finger, using it as a center.
Another way is vibration, which comes from the shoulder with more straightened hand. The thumb feels almost as a "slapping swing" used in funk bass guitar. That kind of technique is especially appropriate to something like most of say, Schubert Wanderer Fantasy, or a lots of Liszt.
I never take the thumb off the keys (well, as well as any other finger--the closer to the keys we stay, the more efficient work. If we raise the finger it means we lost time twice (going up, and then back), which also takes mental attention from the most important thing, i.e. matching the image in your head with what you hear.