I just picked up a violin for the first time in what must be 25 years. All that time ago, I had lessons and playing in school orchestras - but moved on to other instruments.
As a beginner I would use open strings to play the corresponding notes.
As a more experienced guitarist/bassist I often avoid open strings, because when fingering a note with the left hand, I can add vibrato, muting etc.
Violinists do a lot of vibrato. Would a reasonably advanced violinist play any open strings at all?
IANAV, but from what I've seen it depends on the kind of sound they want. An open string sounds so different that if you want a consistent sound for example for a melody line, you'd try to avoid it. In a fast scale it doesn't matter that much. Open strings can also be used to get certain effects, like a folk fiddle kind of sound or just a stronger sound. In short, open strings are used, but not mindlessly.
As for vibrato, they can do some kind of vibrato even on open strings. I believe the vibrato is done on another string an octave higher which then causes the note to vibrate due to sympathetic resonance or something. Or if you vibrate the whole instrument really vigorously, you can use the doppler effect... ;-)
Yes, violinists use open strings. I originally trained in Strathspey and Reel violin, and we would not only play fingered notes, but would also alternate open drone notes with high notes, or even play multiple strings at the same time.
Vibrato is also not mandatory, it it's used a lot but some pieces require none, and in fact a better violinist needs less vibrato to hit the right notes.
Yes - they use open strings (I am a violinist.) They don't use them all the time however, and a competent violinist will make the decision as to whether to use an open string based on the type of sound required. An open string will often give a brighter, more open sound, which can sometimes stick out like a sore thumb and other times really enhance the melodic line.
As pointed out already, vibrato isn't always required, and IMO is used way too much these days (Bach with vibrato? Really? Really?!) You can do open string vibrato, though personally I avoid it whenever possible, it's a subtly different sound to normal vibrato and doesn't sit well with my ears. Generally for this reason, I'll often use open strings much more in Baroque and early classical than with later works, since I find the sound often fits better. This is of course by no means a hard and fast rule though.
Now here's an example of a well-known open-string note: the second theme of the first movement of Mendelssohn's Violin Concerto. The soloist has to hold a low G for several measures. There's only one way to play it, and that's on the open G string. That G string had better be perfectly in tune!
