When writing about violin players furiously bowing their strings, it has become a bit cliché to evoke the image of “rosin flying into the air” as a display of ecstatic music-making. It’s easy to find that that phrase in countless journals and books ... but what exactly is rosin for?
Rosin starts as resin, a sticky and viscous substance of trees that at first glance is not unlike sap. But while sap has more nutritional uses (syrup, for instance), resin is used to make things like glazes, plastics and varnishes. Rosin is resin in its solid state, produced by removing wood fibers from the resin, distilling turpentine from that byproduct and refining still further. (For more on rosin’s journey from tree to violin case, check out this Strings magazine article.)
So let’s imagine you’re a violinist and you’ve just been handed a brand new, un-rosined bow. If you were to use it, you’d notice right away that your instrument refuses to produce sound. That’s not because it hates you or refuses to obey, it’s because there’s very little friction between the un-rosined bow and the strings, as illustrated in this video:
The sound is barely perceptible, but once rosin is introduced, you get sweet friction and a mini-music miracle. In order to explain why, we must take a closer look at the bow itself.
There’s no evidence of exactly when humans started running bows over strings, but Grove notes the practice probably originated in Central Asia, and was established in the Islamic world and Byzantine Empire by the year 1000. Horsehair bows are indeed made with actual horsehair— optimally from the tails of Central Asian stallions (horses bred in northern climates producer stronger hair, and stallion tails are generally cleaner than those of mares, which are more likely to be occasionally blasted with urine).
Now that you’ve got your history for the day, it’s time for some histology — the study of tissues on a microscopic level. This video by violinist, adjunct professor, biomedical engineer and San Antonio Symphony substitute Sharon Kwee that looks at horsehair on a microscopic level is a great place to start. Even though it’s titled “The Science and Engineering of Rosin” she spends a considerable amount of time talking about hair since, as you’ll see, it’s pretty hard to separate the two topics.
Horsehair has several apparently raised scales on its surface, and one might assume those imperfections latch onto the string, gripping it to initiate the vibrations that produce sound. The actual impact of this structure was at one point controversial enough for acoustical engineer Françoise Rocaboy to publish an article in a 1990 issue of the Catgut Acoustical Society Journal (yes, it’s a thing), in which she presented several micrographs of bow-hair in order to support the “flat scale structure theory.” In other words, she argued that horsehair isn’t covered in kinks and barbs that latch onto strings because they can’t latch onto them. As Rocaboy argued decades ago and Kwee points out above, these kinks aren’t actually raised enough to latch on to the strings — they’re only about five micrometers high, insanely small evenwhen compared the .2mm to .8mm strings of a violin.
But when rosin is applied to the hair, there is a dramatic change: those scales are covered in particles of rosin.
When a rosined bow is drawn across strings, the rosin’s stickiness creates enough friction to create a grip on the string, pulling it further away from its resting position until it snaps back into place — only to be pulled once again thanks to the continuous bowing motion. Of course, all of this happens rather quickly, and if you are able to visually perceive that action something is either wrong with your violin or you need to put those superhuman powers of yours to better the welfare of your fellow humans.
A few final facts:
- Violinists don’t need to rosin-up every time they pick up their instrument; a single application can yield sound for a few hours of playing time.
- Several types of rosin are available, and the type used depends on the instrument in question.
- Gold and amber rosins are tapped from pine trees in the late winter and spring. These are ideal for violins, violas and performances in humid environments.
- Darker rosins are tapped in the summer and spring. They’re much stickier, making them ideal for pulling the lower notes of the bass and cello, and in chillier situations.
- Richard Ward of Ifshin Violins is quoted in Strings saying any type of rosin “pretty much works on any instrument.” Unless you’re dealing with a bass. In that case, always grab the dark stuff.