Q: What is the difference between a viola and a violin ?

A: The viola burns longer...

If Hermann Helmholtz could be wrong about some of this stuff then I have no doubt that people are capable of deluding themselves in to having the ability to hear things that aren't there.

From "The Acoustical Foundations of Music" by John Backus, page 207:

For example, the excellent quality of Stradivarius violins has been attributed to a varnish of almost magical properties used by the old instrument makers, whose secret has been lost. However, resonance curves made on instruments in the varnished and unvarnished condition show that as normally used, the varnish itself has rather little effect on the tone.

What effect it has is more likely than not to make the instrument worse.