Any useful finish is going to be a harder material than the soft early wood in the top. A coat of finish on the top will thus tend to add a certain amount of stiffness across the grain. Even a thin layer has an effect, since the tension/compression forces when the wood bends are highest in the surface layer. Schleske put some numbers to that in his 'On the Acoustical Properties of Violin Varnish' in the 'Journal' of the Catgut Acoustical Society, Vol. 3 #6 pp 27-43 Nov. '98. I'll note that his 'violin varnishes' included at least one sample of nitrocellulose lacquer as well as shellac. I suspect this surface stiffening effect is what Bruce is hearing.
I'm still brushing oil varnish, and seem to get a reasonably consistent film thickness of .0025" or so. Note that due to the slow cure rate of oil varnishes this will not stay level; even wood movement with humidity changes will show. That super level show car finish really needs more material. Ovation tops don't show much wood grain, but they use as much as .04" of epoxy....
Last edited by Alan Carruth; 06-28-2020 at 11:09 AM.
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