| Well, let me try and describe this as best I can. From arco, you want to release the grip of your thumb and first two fingers from the stick, and, while letting the bow drop downwards, hook your pinky into the crook of the frog, so that the bow is effectively held between your pinky and ring finger, pointing at the ground. you are now free to pizz with your first two fingers (a nice upside to german bow, in that you can excecute electric bass-style double-finger pizzes while holding the bow.) To return to arco, its a bit of an acrobatic motion, so you're going to have to spend some time practicing going back and forth (I'd use a mirror), you sort of "toss" the bow back up using both your thumb (pressing outward, that is away from the bass) and your fingers. I don't mean like, fling it, just sort of flick it back up into a parallel-to-the-ground position. The trick then is to get your fingers back into a proper bow grip. I'd suggest just practicing going back and forth a bunch of times till it feels comfortable. If you're new to german bow, it might take a while to get used to. Hope that helps, and it's just the way I do it, so don't take it as gospel.
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"I know, sir, that I have played out of tune, but once I learn where to place my fingers, this will no longer happen." - Giovanni Bottesini, on botching his conservatory audition.
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