Frank Weston wrote: > > To refinish, rub or brush two or three coats of cut orange shellac onto > the board. Polish if you must. This finish is quick, easy, and > authentic. Reblitz says to add a coat of varnish, but I think this is > unnecessary. Most of the vintage soundboards I have seen needed > refinishing because of dirt, scratches, and cracks, not because the > shellac had deteriorated. It the shellac is good for 90 or so years, > why attempt to improve on the process? > > Frank Weston 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. 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. 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.) 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. (The only finish material I have ever tested that did produce a measurable and audible change to a soundboard was polyester. It both stiffened and loaded the board enough to produce audible changes in tone. Epoxy was not considered a viable wood finish and was not tested as such. Applied in the thickness required to provide a complete vapor barrier, I suspect it would test much the same as polyester.) So, assuming that the customer wants the color of a traditional soundboard finish, then a finishing schedule using a shellac base plus two coats of good quality varnish (sanding between coats is required with varnish) has much to offer. It will provide all of the benefits of a good wood finish and also provide the color and beauty of a traditional (aged) board. ddf
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