That old upright may still sound great, but those yellowed keys definitely hit a sour note. Remove age stains on your ivories by mixing a solution of 1⁄4 cup of bicarbonate of soda in 1 litre of warm water. Apply to each key with a dampened cloth (you can place a thin piece of cardboard between the keys to avoid seepage). Wipe again with a cloth dampened with plain water and then buff dry with a clean cloth. (You can also clean piano keys with lemon juice and salt.)