What makes strings sound "sweet"?


I have always wondered about this. If you listen to many recordings of bowed string instruments, then you know that the upper registers can sometimes have a sweet tone. I define this by what it is not - edgy, brittle, dry and rough sounding. It is smooth and inviting. I used to assume this was due to rolled off highs or an emphasized midrange, but I am not so sure. It varies by recording, or course, but I have often wondered what, in the recording or reproduction process, causes strings to either sound brittle or sweet. Is it the acoustic of the original recording venue? A frequency balance issue? I would love to hear from those who might know. Thanks!
bondmanp
Of course woods and varnish have a role as with the overall size of the instrument as well. Horsehair bow vs. synthetic. Type of rosin used, ivory frog vs. plastic/bone frog, type of wood in the bow, etc..etc. The player is probably one of the more important keys. A good player can help a not-so-great instrument sound just a little better.

Citing all of this I think it is nearly impossible to obtain a perfect recording, unless you are Maxim Vengerov or Hogan. Then you are just perfect whether it be an iPhone recording or professional. ;-)
Good responses, but if we already have a well-recorded section (either live or a good VI like Vienna Symphonic or Hollywood Strings), how do we get a sweet Montavoni or Mancini sound? I *think* this is an EQ question and I am hoping for guidance.

Regarding the various harmonics in the series, I am impressed by the knowledge here, put I don’t know of a simple technique to alter harmonic content selectively.

A practical answer would be greatly appreciated.
Example of what I mean: I’m sure varnish is something of a factor, but I don’t think we can control that, and I doubt producers recording strong sections look into that.
I am not a musician but my daughter does play violin and the sound can be sweet or strident naturally it seems depending on technique, sometimes by design sometimes not.

I am also pretty confident not all violins or string instruments in general all sound the same in this regard. 

Plus when it comes to recordings, the production technique used also affects what is heard in the recording in this regard.    Are there two violin recordings where the violin sounds exactly the same out there?