Use Lubricated Sandpaper
In the case of authentic antiques, it's always preferable to avoid removing or destroying the original finish. However, if the piece you're restoring has a finish that's been severely damaged -- to the point that it has actually become rough and dry -- there's a fairly dramatic measure that might be taken.
To smooth the rough surface without destroying the original finish, consider using extremely fine sandpaper in conjunction with lemon oil. In our demonstration, 600-grit sandpaper was used. Since even a grit this fine can scratch the finish, it was used in conjunction with some ordinary lemon oil. Apply lemon oil to the sandpaper (Image 1) as well as to the finish itself. The objective is to avoid sanding away wood, but to remove some of the dead finish.
Once the oil is has been applied, use the lubricated sandpaper to gently sand the top layer of finish (Image 2). This technique should result in a finish that's very smooth, and which brings life back to the aged wood.
Since the lemon oil simply acts as a lubricant, wipe it away with a clean rag once you're done sanding (Image 3). If done properly, this is a safe technique for restoring a badly damaged antique finish while helping to rejuvenate the wood.