Some Bow info:
The traditional explanation of the hair on the bow has been that it has a rough surface that is like little hairs. Rosin makes these separate and stand up, and gives them a sticky quality. They can then grab the string like millions of fingers playing pizzicato. While this is a nice metaphorical explanation, this model has been revised, as can be seen here:
As the bow moves, there is a pull and slip (called a Helmholtz motion) that allows the string to vibrate back and forth, like this:
Too much rosin inhibits the slip, too little inhibits the pull. Neither sounds good. As a general rule, a little bit of rosin applied regularly is all you need. If you are getting a bunch built up on your strings or the top of your instrument, you are probably using too much.
As to tightening the bow, you need enough tension on the hair to grab the string and so that the hair does not touch the stick when you play. Generally speaking, a very flexible stick needs to be tighter than a stiffer bow.
The color of the hair is not a fair gauge of whether it needs rosin, horse hair has different shades. The best way to judge if you need rosin is by how it feels to use the bow. If the sound is whistle-y, does not speak, etc., you need more rosin. If clouds of rosin puff up when you play, it is way too much. As you are learning, just put a few swipes on each time you play and see how it feels. If you get a bunch left on your strings and cello, wipe it off with a soft cloth and skip rosin for a couple of days and see how it feels.
Cleaning up rosin
Tips on buying a bow
Go to a bunch of violin shops or bow makers (not “music stores”) and take your cello with you. Try as many bows as you can on your cello and see what works for you. You will learn a great deal from this. Brands are irrelevant, sound and handling are all that matters, what is good for one cellist on one cello does not necessarily transfer to another.
Try to have a colleague go with you to try bows on your cello, as hearing the sound of different bows on your cello as a listener is also important. Look for flaws in the bow by playing long, slow bows, and if you see the bow “jerk” a bit consistently in the same part of the bow, that can indicate a problem. Of course spiccato, sautille, etc. are important to test.
Lots of shops will send out a group of bows on trial, so decide what you want to spend, and contact the big shops that offer this service. Don’t obsess on names, what you need is a bow that works for you and your cello.
Why is a frog called a frog
There was a great variety of bows during the period 1600 – 1750. Most bows from before around 1720s were bows without an adjustment screw. Instead they had a frog which was wedged between the hair and the stick of the bow. (When not wedged correctly, the frog can jump out of its intended position, and this is what lead it to be called frog, since it had the tendency to jump). Such frogs are usually somewhat higher and are well rounded at the end over which the hair runs. Baroque bows come in many sizes: from very long to very short. This has to do with the many different types of bow hold that existed, from almost at the frog to close to a third up the bow, to underhand grip; all of these different bow holds need a different type of bow. Most baroque bows are convex, but some later ones might be slightly convex toward the tip. Underhand bows tend to be longer and have heavier tips than overhand bows. Different types of wood were used: snakewood is most commonly seen nowadays on baroque bows, but ironwood, bloodwood, some late ones in pernambuco, even light woods like beech and larch have been used to make bows from. All of these of course have a serious impact on how a bow functions, and what they can do for you.
Tensioning and de-tensioning a baroque bow