There is a lot of conflicting advice regarding polishing pianos on the Internet, some from seemingly reputable sources such as the websites of fully qualified piano technicians.
However, one thing that most people seem to agree on is not to use regular aerosol-type furniture polish, even if it is a reputable brand. Leaving aside the fact that the fine waxy spray can wreak havoc with the internal working of a piano, the polish itself might be the wrong kind of polish for your piano.
Pianos usually have a lacquer finish or a polymer finish, and using the wrong polish will do more harm than good. For the trained eye discerning the difference between the two types of finish might not be difficult, but if your experience of polishing wood extends no further than polishing furniture with a household spray polish, it’s best to seek professional help. A qualified piano technician is a good person to turn to, but if you decide to polish your piano in between visits from your piano tuner you need outside help.
The safest solution is to forget using this wax or that wax, car wax or a damp cloth with a drop of lemon, and go to a music shop – preferably one that sells real pianos – to buy a propriety cleaning product. This is something I did after acquiring an old, very dusty, piano. In the piano showroom I was able to describe the finish my piano has and point to one that looked the same. I was immediately given the right kind of polish.
Some piano makers sell polish specifically for their pianos, which surely must be the safest bet if you want to restore the original gleam. The polish itself isn’t expensive. In fact I picked up the polish and a soft cleaning cloth for less than £10.
With regard to the actual polishing technique, applying polish to the cloth, and not directly onto the piano, seems to be good advice, as it reduces the possibility of unsightly streaks.
However, before you go to any of these lengths it’s worth asking yourself if your piano really does need polishing. If it is already shiny it probably doesn’t, and lightly dusting with a soft cloth should be enough to remove any fingermarks.
Of course bleach or any other household cleaning chemicals should be kept well away from your piano. This includes solvents like alcohol and paint thinners, which can easily damage the finish.
With just a little care and attention your piano case should stay looking good for many years.