Basic bow stroke technique - violin and viola
The key to developing the basic bow stroke is to keep the bow parallel to the bridge as the student moves the bow from the frog to the tip of the bow. A bow stroke that does not move parallel to the bridge will not produce a full and resonant tone. The bow stroke should be extended gradually so the student can develop a feel for the motions described below.
The basic bow stroke involves the following motions:
1) The shoulder joint is flexible. The elbow opens to an increased angle as the bow moves from frog to tip (downbow). When the bow is at approximately the middle, the elbow will be at a 45 degree angle. As the bow moves from tip to frog (upbow) the angle of the elbow decreases, as shown in this video.
2) The wrist will pronate as the bow moves from frog to tip, and supinate as the bow moves from tip to frog.
3) The fingers flex as the bow moves from frog to tip. The 2nd joints on the fingers (the knuckles) are the least bent when the bow is at the tip and the most bent when the bow is at the frog.
Notice that the upper arm is relaxed, but moves only slightly. If the student moves the upper arm without involving the elbow, wrist, or finger hinges, the bow will not remain parallel to the bridge.
The fingers must be curved and flexible.The fingers must stay in one contact point with the bow and flex, not move to a new position on the bow. Holding the bow must be accomplished with the least amount of squeeze on the bow. As Suzuki said, "Hold the bow tightly, but lightly."
Some teachers prefer to describe the bow angle as "perpendicular to the string" instead of "parallel to the bridge."