History lesson: Before the 1960's polyurethane, and waterproof finishes did not exist. Finishes before the 1920s were usually many layers of orange shellac. From the mid 20's to the late 30's dark finishes became popular, this time made of wood stain with layers of shellac on top. (Look up French polishing, this is the type of finish on your piano.) Over time shellac becomes dull and darkens with age.
Older finishes have cracks and blemishes unable to be seen with the naked eye. If you were to put Murphy's oil soap on it, your finish would turn cloudy and it's a real PITA to clean off. Take a clean rag and get it wet and then wring as much water out as you can (Too much water and your finish will turn white) and then put a drop or two of dish soap and wipe it down gently. Don't rub too hard, especially on the two arms that stick up at both ends of the keyboard. ( people usually rest hands and arms there so the finish will be softer) Then get a good hard paste wax (Like what you would use on a car) and do one surface at a time, rub on and then polish off. 2-3 layers on each surface and it will look brand new!
If you ever plan on refinishing it, never ever use pledge, or anything like it.
*If your finish has an alligator texture to it*
Just wipe it down, but don't wax it. You will have to live with it.
