A bow which is being used regularly generally has to be fitted with new hair at least twice a year. Over-used hair has lost it's capacity to hold the rosin properly and the player will notice the bow's lack of efficiency to produce a good tone.
It is often heard that horsehair for bows must be quite white and exceptionally smooth. While it is true that irregularities in the hair's structure can cause noise, hair is a natural material and is seldom perfect. Completely white hair is very rare unless it has been bleached. The hair's whiteness is not neccessarily it's most desirable attribute. Often the finest hair is anything from light-beige to butter coloured. Bleached hair is generally brittle and should be avoided as it doesn't last very well. Fine bowhair is exported from Canada, South America, Australia, China, Japan, Hungary and Russia.