[ Ref. 120410 MMDigest, Traditional Piano Finishes ]
The sure test for shellac is to rub a cloth dipped in methylated
spirits -- on the back of a leg, for example, where it won't show --
and see if it dissolves the finish. Sunlight and heat are notorious
for crazing French polish, though I don't know if it's the same for
nitrocellulose lacquer. Before I treated it, my Edison Diamond Disc
phonograph looked like a crocodile skin -- most unfashionable!
Shellac comes in many grades, which give different colours, e.g. garnet
(reddish), blonde (clear), lemon (yellow), button (brown). Though
you can add a few drops of stain, I prefer to use the various polishes
on their own or mixed to get the desired colour. You are fortunate
that the makers have not stained the original bare wood, as this is
naturally difficult to remove; this gives you much greater flexibility.
In the 1920s, shellac could have been sprayed on, but in the UK at
least (probably earlier in the USA) by the mid-1920s, shellac began to
give way to cellulose on phonographs.
Good luck, hope this helps.
[ At http://en.wikipedia.org/wiki/French_polish : "'French polish' is
[ a process, not a material. The main material is shellac, ..." More
[ information at http://www.mmdigest.com/Archives/KWIC/S/shellac.html
[ -- Robbie