What is rosin? Basically, it is just melted, filtered tree sap. As a kid, when you went climbing in the pine forests and got that sticky sap all over your hands, that is the base ingredient of most rosins. It is collected from certain trees, melted down under a low heat as to not burn the sap, sent through multiple filters to clean out all of the unwanted particulates, sometimes different things are added to the rosin, like precious metals, or chemicals, then poured into a mold and left to cool and harden.
Pouring rosin into a mold
There are a lot of bow rosins on the market. Different thicknesses of strings uses different kinds of rosin. Generally, the thicker the string, the softer the rosin should be.
Student rosins are often cheaper, produce more powder when used, and are suitable for beginner students, as well as fiddlers. Most classical violinists prefer professional grade rosins, as they usually produce a smoother and more controlled tone.
Rosin is usually categorized as light or dark, but is sometimes named for the season of preferred use, summer (light) or winter (dark). For violin and viola, light colored rosins are preferred, as they tend to be more dense and harder. They are also not as sticky as their darker counterpart. They produce a finer powder capable of grabbing the smaller strings. Dark rosins, being very much softer, are used for thicker strings, especially bass strings. They are also used more in cool, dry climates, as they will tend to become gummy in hot and humid conditions. Dark and light rosin both start as the same, a light amber yellow color. To make a darker rosin, the sap is heated to a higher temperature to actually burn the rosin, causing it to darken. Because the rosin is burnt, it never fully hardens again, causing the rosin to be slightly softer.
To confuse many people, most rosin companies will come out with a dark and a light version of the same rosin.Hill rosin is the perfect example. It comes in 2 different versions, light, a honey-amber color, and dark, a licorice black color. After testing the 2 rosins, I can spot absolutely no difference. One feels no harder than the other when I try to dig my nail into the cake, and the other feels no more sticky when bowing than the other. That being said, I have a particular brand of dark rosin I have come to love, and have tried many different brands and colors, never giving me the sound and feel i was looking for.
Most players will experiment with different rosins within their first few years of playing, and eventually find a rosin and stick with it for the rest of their lives. Many do not try out different rosins, or new ones coming onto the market.
A word of warning about trying different rosins on a bow. It can take anywhere from 50 to 70 hours of playing to actually change rosins on a bow. Because the change is so slow, many do not notice a difference between rosins. The best time to switch is when you get your bow rehaired. This way you will be able to note the differences right away.
Some rosin makers add precious metals - gold, silver, lead-silver, or copper - to their formulas. These metals will aid in producing different tonal qualities. Gold rosins are generally preferred by solo violin players, as they will help to create a clearer and more focused tone. These rosins can also help to soften a harsh sounding instrument. Gold rosins are suitable for almost all instruments, helping them to produce a warmer and crystal clear tone. Rosins with silver help instruments like the violin and viola to project a brighter and more focused tone. It also can help brighten a darker or more nasal instrument. They are not used for thicker strings like the cello and bass. Lead-silver rosin is used for the violin and viola, and helps produce warmer tones. They are soft, but unlike most dark rosins, they are not super sticky. Copper rosins are best suited for beginner violins, especially fractional sizes. They help the students to play easier by reducing the scratchiness of some smaller instruments. Copper also helps produce warmer tones.
Clarity colored synthetic rosin
New to the market are synthetic rosins, made of a combination of different chemicals. Most of these rosins will by hypoallergenic as well. So if you begin to get contact dermatitis (rash) with use of a standard, natural rosin, try one of these. Some synthetic rosins can come as a clear cake, or have different colors. There are some other rosins that have both the natural components like filtered tree saps, but also have certain additives such as proplene-glycol to help enhance the tonal properties of that specific rosin, Jade Rosin is a perfect example of a partially synthetic rosin.
Bass rosin is graded by its hardness on a scale of I-V, and can be either light or dark. Bass rosin is very soft and sticky to be able to grab those thick strings. Some bass rosin is so soft, that when the container is left open on its side overnight, the rosin will "pour" out of the container!
If you don't know what to choose, talk to your local string expert. They all will have their favorite and will help you make the best decision to fit your playing abilities, style and instrument setup.