Bows for string instruments are made of a pliable wooden rod with horse hairs stretched from the bent head to a moveable nut used for tightening. The hair part of the bow is drawn across the strings, thus setting them in vibration.
The term bowing has a two fold meaning. It refers to the continuous and alternating movement of the bow on the strings as well as to the markings that are used to indicate the direction of the bow. Thus bow markings determine not only the manner in which the bow will be used but also the style or phrasing of performance.
The degree or strength of tone, for the most part, depends on the amount of bow used, along with its placement and pressure on the strings.The string player divides the bow into three parts: the upper third near the tip, the middle, and the lower part near the frog or nut.
These distinctions may have a practical application and understanding through working out the following experiment.
Balance a violin bow on the finger by finding its balance center. Notice that this center is not the exact middle of the bow: The weight of the bow causes the balance point to be a little toward the lower end. This experiment establishes the frog-end of the bow as the heaviest part. However, when string players place their bow on a string in playing position, they automatically center it. This playing center is used mostly for passages in the middle range of dynamics (piano, mezzo-piano, mezzo-forte).
Now draw the bow over an edged surface. As the bow moves toward the frog notice that it is possible to exert considerable pressure on it. This lower third of the bow is best suited to the stronger dynamics ( forte, fortissimo, etc). It is ideal for sharp, dry, brittle parts that require strong accents with short bows.
Finally draw the bow in the opposite direction toward the tip and observe that as the upper third of the bow is reached, the amount of pressure decreases to practically zero. This upper third of the bow is usually reserved for al of the softer dynamics with little or no expressive overtones (piano, pianissimo, etc.).
From this resume, it is clear that position of the bow on the string has considerable to do with the degree and variety of tone that will be produced. This simple explanation can be of definite value to non-string players who must struggle with bowings as an integral part of a scoring technique.
Excerpt from: Orchestration by Joseph Wagner
BOW MAINTENANCE
Do not touch the hair on a vioin bow with your fingers. The bow will not contact the hair properly if you do.
Tighten the hair on the bow enough so the hair will not not touch the stick when played. About the width of the tip of your smallest finger.
Rub a small amount of rosin on the bow hair so the bow will produce a sound and not slip on the strings.
Loosen the hair on the bow when you are finished playing and putting it away in your case.
When the bow hair is worn smooth and does not produce a good sound it should be rehaired by an experienced luthier.
Sometimes the bow will no longer tighten or lossen, the bow also needs rehaired when this occurs.
No not let the thumb pad wear away, replace it when it begins to wear, this protects the stick from damage.