Many violin pupils either do not rosin their bow enough, or else do it in such a way that much rosin collects on the body of the violin under the strings. The first method produces squeakiness, and the second scratchiness--besides interfering with the vibrations of the instrument, and thus marring the tone. The bow should be thoroughly rosined with good rosin. Then loosen the hair and shake the bow, whipping it through the air several times. This forces the powdered rosin to go between the hairs instead of merely on the surface. When good rosin is used, this is all that is necessary; if cheaper material is used, it may be necessary to blow the waste matter from the hair after it is tightened.