John Tuttle wrote:  "When I was an apprentice at the Tusting Piano Co.,
I was told that all circa-1920 pianos were finished with varnish, not
shellac."

If you are not sure whether your piano is finished in varnish or
shellac, just wet your finger in alcohol and rub it on the old finish
in small circles.  If orange/brown comes off on your finger, then the
piano is finished in shellac.  Varnish will not melt with alcohol.

I find that many of the old guys use the terms varnish and shellac
interchangeably.  As far as I know varnish did not come into use until
the late 'thirties or early 'forties.

D. L. Bullock    Piano World    St. Louis