Rosin is basically the same substance that you see pitchers use on the pitching mound in a baseball game to increase their grip on the ball. It is generally produced as a refining by-product while distilling turpentine from tree saps (mostly various species of pine) - it’s the goo that’s left after the spirits have been evaporated off. Contrary to many old beliefs, the hair does not have microscopic hooks that are raised up by rosin. Under a microscope, the hair looks like a swamp reed, with slightly ragged growth rings that themselves don’t have enough friction to do any more that just tickle a whisper from a string. However, they do have enough friction to provide a way for the rosin to transfer and hold to the hair. Once there, the rosined hair will begin a succession of “grab and release” catches of the string to cause a somewhat sustained vibration of the string.
As a somewhat general rule, darker rosins tend to be softer, melt at a lower temperature (like in the summer sun), and grip better in colder weather. Very light rosins tend to be just the opposite: harder, work better in warmer weather where a darker rosin might tend to soften and became gooey while playing.
If too tight, move the peg of the bow left until the wood is straight. If too loose, move the peg right so that the wood does not sag.
Wash your hands beforehand so you don’t get your rosin dirty. Be sure you also wash your hands after because your hands will be sticky and messy with rosin dust.
Gently, and with little pressure, brush the hair of the bow against the rosin. One stroke down should end with the tip of the bow (the other end) next to the rosin. Then, go backwards so that the frog is next to the rosin again. Repeat up and down strokes five times. Be careful. Don’t “play” the rosin very quickly, or you’ll risk breaking the bow. The new bow is not yet used to the high tension.
Remember to maintain the same amount of pressure through out the strokes. Change in pressure will cause some parts of the bow to play notes clearly and others not as clear.
If the violin still does not make noise again after rosin is put on, put more rosin on until notes are heard clearly.
