Photo by: Violin Masterclass
According to the Merriam-Webster
Dictionary, a harmonic is best described as "...a
flutelike tone produced on a stringed instrument by touching a
vibrating string at a nodal point."
Harmonics are created by lightly laying your finger across the vibrating string as you play. Your finger will transfer very little weight onto the string, and will not be touching the fingerboard at all. You will be able to feel the vibrations in the string very well, because you are not exerting the typical amount of necessary force. When this happens, there is an audible widening of sound that occurs. Violin Lounge, a website specifically for violinists suggests that that one of the best ways to play a clean harmonic is to "use more bow speed". They have written that "If you bow slowly, it's harder to make the harmonics work on your violin." As a violinist, I can vouch for this statement. If you bow slowly, the harmonic will be scratchy and might not make any sound at all. The trick is to use more bow speed, and then the harmonic will project cleanly.
A short video that gives helpful explanations regarding frequencies, sound waves, and harmonics has been included below. Even though it uses the piano as an example, rather than an instrument such as the viola, it gives the listener an idea of that the harmonic series is all about.