No-one seems to have answered John McClure's query about cleaning a
piano, so I will offer the following.  I have a book about staining and
polishing, and it offers a couple of 'recipes' for polish revivers.

The first recipe is 1 part vinegar + 1 part raw linseed oil.  The idea
is that the oil removes grease and wax deposits but leaves a film of
oil, and the vinegar helps prevent the film and brightens up the
finish.

The second recipe is simply the further addition of 1 part methylated
spirits (i.e. the spirits used in French polish).  This will gradually
take off the underlying French polish (assuming that is what the piano
was varnished with), so needs to be used carefully.  It is good, however,
on items where the wax polish has sunk into the French polish.  In both
cases the solutions need to be well shaken to form a sort of emulsion.
Use a soft cloth round and round and up and down 'til you get the
desired effect.  Turn the cloth frequently as it collects the dirt.

I will admit that I have not used these on pianos, but I have used them
on other antique items to good effect.  The main thing is to progress
slowly and rub lightly, so you only remove what is necessary to get the
brightness back.  The finish may be left a bit dull, so will require
refreshing with a new layer of good quality wax (not silicon) use a wax
made for antiques, probably based on bees wax, or carnauba wax.

If possible, try it out first on a small insignificant part of the case
(might be difficult on a piano!), just to make sure everything is okay
and to perfect your technique.

John Farmer
Worcestershire
UK