What makes a quality violin bow well...quality?

several things make the difference with a violin bow and therefore the sound of the violin. A Violin bow was made exclusively from strands of Horse hair from it's tail. the finer and the stronger the hair, the sweeter the sound. There is argument now that some of the synthetic fibres rival the highest quality horse hair. The wood that the bow is made from is also important, and the "nut" which provides tension to the bow, some have to be continually re-tightened, whilst more precision bows will last for hours without adjustment. hope this helps. by the way, unless you are playing in a world class orchestra, save the money and buy a cheaper bow, the price difference is enormous.