Authentic Steinway sound board dilemma

[Delwin D Fandrich]

Frank Weston wrote:
> 
> Delwin D Fandrich wrote:
> > A finish that provides a good—even though, admittedly, not perfect—vapor
> > barrier goes a long way toward reducing the extremes of internal
> > compression and tension that a soundboard would otherwise be subjected
> > to. If the finish is able to resist the movement of water vapor well
> > enough, it will slow the wood’s absorption of moisture, often long
> > enough to allow the humidity level to return to a more moderate level.
> > Both modern lacquers and varnishes are able to do this. Shellac is not.
> 
> Del, I don't mean to be argumentative, but this last statement sounds
> largely conjectural.  It appears to me that the rate at which
> atmospheric humidity changes would have just as great an impact as the
> rate at which the surface coating transfers water vapor.  

No, it's not conjectural. I once did a series of test to determine which
finishes would be best for piano soundboards. In a sense the results
were inconclusive in that there wasn't a lot of difference between the
various film finishes such as lacquer and varnish. There weren't enough
samples in the to statistically prove the superiority of one specific
product over another. Both varnish and lacquer slowed the growth and
shrinkage rate of the wood in response to an accelerated aging test. It
was a lengthy and time consuming project and  which I have no
inclination to repeat—at least not at my expense. Of course, if someone
else is willing to pick up the tab..., well, money talks.


> I rely upon
> empirical evidence when I draw my conclusions about shellac finishes on
> soundboards.  I have encountered many vintage pianos with shellac
> finished soundboards that were perfect.  I have in my home/shop now one
> 1922 Steinway M and one 1912 Knabe B that are good examples.  I have, on
> the other hand seen lots of new and old pianos (shellac finished and
> otherwise) with badly cracked and ridged soundboards.  Is shellac the
> reason some soundboards last?  Maybe not, but there is certainly
> evidence that shellac does no harm, and lasts a long time in this
> particular application.

I too have observed this phenomena but must suggest that the longevity,
or lack thereof, of any specific soundboard depends more on how it was
originally bellied than on the finish used to “protect” it. Soundboards
that are “compression–crowned” (as were most pianos built before the
1950’s or so; some still are) live on the edge of destruction from the
day they are born. While a shellac finish may not do much harm in and of
it self, neither does it help much. Well, one could make the observation
that simply by not helping, it is causing—or is at least allowing—
unnecessary harm to come to the soundboard panel.

A finish that provides a vapor barrier does help to stabilize a
soundboard during periods of humidity fluctuation. None of these
finishes are perfect, but they do help. No finish will prolong the life
of a compression-crowned soundboard indefinitely. I suspect that those
few (compared to the huge numbers built) older pianos that have survived
with soundboards that still look good—as opposed to sound good, which is
not the same thing at all—had a somewhat higher moisture content when
they were ribbed than did their contemporaries. These boards would
naturally have somewhat less internal compression and, as such, would be
inherently less prone to compression failure.

When attempting to form general rules of behavior—whether of wood or of
people—it’s a good idea to use the mass of evidence as a basis and not
single out just a few exceptional examples. Although I have also caught
myself doing so, it’s not very reliable to use the survival of the
exceptions to form generalizations that otherwise contradict the
evidence provided by a much larger number of failures.

In any case, all of this stuff is based on fairly some fairly
fundamental rules of wood technology, though most piano folks would much
rather believe wood mythology. Sadly, not even the poetic Lac bug has
been given the power to rewrite the laws of physics.

ddf