Authentic Steinway sound board dilemma

[Frank Weston]

Delwin D Fandrich wrote:
> 
> 
> Frank,
> 
> Actually I can think of several reasons to use something other than—or
> in addition to—shellac alone for a piano soundboard finish.
>
> The purpose of any wood finish is basically threefold:
>   1)  It should enhance the beauty of the wood.
>   2)  It should protect the wood from physical damage.
>   3)  It should provide a reasonable vapor seal to protect the wood from
> changes in humidity and by so doing help to stabilize the wood against
> dimensional changes. In my view, this is probably the most important
> requirement for a piano soundboard finish.
> 
> To this list could also be added a fourth requirement: the finish itself
> should be reasonably durable and resistant to ordinary household
> chemicals and physical damage.
> 
> At its best, shellac fulfills only one of these requirements. It
> does—and, here I agree with the traditionalist—enhance the beauty of the
> wood, although I must add that even this is debatable. Surely this is a
> purely subjective preference; there are some, if not many, who do not
> care for the relatively dark orange color that shellac gives to the
> soundboard.
> 
> Other than that, however, shellac fails miserably as a wood finish.

Del,

When you attack shellac, I must spring to the defense.  In my finishing
book, shellac is one of the most useful, flexible, user friendly,
beautiful, safe, reversible, inexpensive, environmentally friendly,
durable, repairable, and all around amazing finishes known to man. 
Shellac can be brushed, padded, sprayed.  It smells good, cleans up
easily, and, in hard times you can even eat it.!  Shellac is compatible
with almost everything.  It is possible to coat shellac over just about
any other finish, and shellac has the highest adhesion and stain
resistance of any common finish.

Shellac is fast drying, shellac is wonderfully clear, and a French
Polish shellac finish it "the" finish to which all others aspire. 
Shellac is an excellent sealer as well as finish coat, the best for
sealing in fish-eyes caused by silicone polishes.

Further pianos of the golden age were finished EXCLUSIVELY with shellac,
no varnish, no nothing else.  I have seen a number of well preserved
specimens approaching 100 years of age with shellac finishes that were
still perfect.   

> Its
> film durability is very poor. It scratches easily and it is very poor at
> resisting abrasions. It is not resistant to ordinary household
> chemicals; even alcohol will melt it. Some household cleaners can
> practically be used as strippers.

Most abrasions that will mar shellac will mar new synthetic surfaces or
lacquer.  The difference is that shellac is far easier to repair.  Yes,
alcohol and water will attack a shellac finish, but a good coat of wax
goes a long way toward defending against these attacks.  Besides, if
you're using your vintage Steinway as a coaster, you deserve what you
get.

> 
> The most serious limitation of shellac, though, is that it is almost
> completely transparent to water vapor. It provides virtually no
> protection against the variations in humidity that a piano soundboard is
> subjected to. No practical wood finish is totally impervious to water
> vapor, but except for basic wax finishes, shellac offers the least
> protection against water vapor of any common wood finish. (Only
> polyester and fairly thick coatings of epoxy can offer complete
> protection against water vapor, but then you no longer really have a
> piano soundboard.)

You said it yourself.  No common coating except epoxy is impervious to
water vapor.  And as you note, you wouldn't want to use epoxy on a
soundboard.  Being permeable to water vapor is like being pregnant -
there is no such thing as just a little bit.  Wood under a permeable
coating will attain a water content in equilibrium with the surrounding
air, no matter what the coating.

> 
> I can think of no good reason for not putting a coat or two of varnish
> over the shellac base. There is certainly no acoustical reason not to.

My basic reason not to is that varnish is not necessary.  Why do it if
you don't need it, and if it will only serve to increase the thickness
of coating on the soundboard?

Here are some general finishing tips with shellac, not necessariy for
soundboards:
Do the first and last coats with very thin shellac and a rag.  In
between, build the coat by spraying or brushing as thick as the climate
will allow. When the finish is built up enough, wetsand with mineral
spirits or naphta, then top off by French polishing.  The results are
unparalleled.

BTW - Shellac is also the best grain filler known to man.  Either rub
the shellac in with raw linseed oil as a lubricant, or mix the shellac
with pumice and work quickly.  Further, spirit stains can be mixed into
the shellac, and the color of the work can be adjusted on the fly.

I must quit now before I begin to wax poetic on the virtues of the
Laccifer lacca beetle who sacrifices his secretions so that we may have
shellac.

Regards,

Frank Weston