I have been thinking of this a long time ago, and I would like to share it to the board and see what thoughts people here may have. I have 2 violins with quite similar set-up, except for some minor differences. Now, when I use one of it to practice for some time, and shift to another, I notice that my finger tire initially for the first few practice sessions, although I can execute the music just as satisfactorily as the other. Now, when I shift to the other violin again after some time using the other one, I notice that the tone that I am producing are far better than before, especially in tonal expressiveness. I mean the vibrato character, and the tonal variation of passages. Now, my theory is this: While some finger and hand muscle groups are strengthened in common using the 2 violins, there may be some smaller fibers that are uniquely strengthened and developed for each. So, what does that have to do with practice? Maybe, practicing on another violin with similar set-up (proper set-up of course), may have a salutatory effect on the sound production since it practices some minute muscles group that are not used, and working of these minute muscles, which we might not at all notice, may help us play the notes and passages more expressively. Playing a passage expressively definitely involves the bowing hand too, but the left hand is just as important, and I suspect that this mechanical thing of producing the sound to give expressiveness is a mixture of different muscle group and fibers at play. This I guess have a lot to do with the unique sound production of different artists. I am thinking, maybe a good way to put these small fiber groups that affect our sound production without our knowing it is to practice on maybe 2 different violins with 2 different set-up. Since I am just an amateur violinist, I have the luxury to experiment, but maybe this is not for professional before performing a concert, when they need just to be thoroughly familiar with the music to be played on their frequently used violin for that particular piece. For amateur, maybe this is a good experiment. Does anybody have any thoughts on these? Or maybe, is it just pure nonsense!! By the way, maybe this concept applies to the right hand too, using 2 different bows. Thanks for any response.