Amongst these are elasticity, transparency, and the ability to improve the tone of the instrument.
Elasticity is an important essential which must be carefully considered.
A good varnish must, in spite of its adhesive character, allow the wood to vibrate freely and should itself vibrate as an integral part of the instrument, and it should not in any way affect the tone possessed by the violin previous to its having been varnished.
It will be seen that if the varnish does not lend itself readily to these conditions and is not elastic but remains hard, it will of necessity tighten upon and compress the instrument, thus rendering the proper production of the sound difficult.
Again, if the varnish does not expand and contract in accordance with the expansion and contraction of the violin, it will crack and so completely spoil the work whose beauty it should enhance.
Transparency, though not quite so important as elasticity, is yet another very necessary quality. An opaque varnish as can be well imagined would be unsightly and absurd.
