How to revive a worn finish
A scratch here, a scuff there, and your eye soon sees the blemishes more than the furniture beneath. Worn doesn't always mean worn-out, though. Anything from a thorough cleaning to a fresh topcoat could cure the problem a lot easier than starting over from bare wood.
Before you treat the problem, though, determine the type of finish you're fixing. First, dab an inconspicuous location with denatured alcohol, shown in below. Shellac finish will come off. If it doesn't, try the same thing using lacquer thinner, which will dissolve a lacquer finish. Neither will affect a catalyzed lacquer factory finish or a varnish.
On newer furniture, you may also have to contend with tinted topcoat finishes. Check damaged areas of the finish: If a scratch changes color without revealing bare wood, plan to refinish from bare wood.
Before you go that far, though, let's try the easier fixes first.
Fix 1: Start with a good cleaning
For light wear and a dingy surface, begin by stripping off old wax, oil, and grime. Wipe the surface using a towel and waterless hand cleaner, such as Gojo or Permatex DL. Dry the surface immediately after cleaning, shown below. Then remove old wax and oil by wiping the surface with mineral spirits.
Now apply a coat of paste wax, such as SC Johnson Paste Wax, to fill in tiny scratches and leave an even sheen. Allow the wax to dry to a haze before buffing it by hand, with an inexpensive car buffer, or with a random-orbit sander and a buffing pad shown in photo below. To avoid damaging the wax finish, don't use spray polishes or "lemon oil" (scented mineral oil and mineral spirits) that will dissolve wax.
Fix 2: Next option: re-rub
If cleaning and waxing don't do the trick, you may need to rub out the finish—a polishing technique. That's only if the existing finish is thick enough, though, because you'll remove some finish during this process. How do you know if it's thick enough? If no scratches penetrate to bare wood, that's a good sign you have enough finish to work with.
Rubbing out an existing finish works much like the final stages of rubbing out a new finish. First, make a polishing pad by attaching a white, non-woven cleaning pad to a sanding disc using adhesive strips. (See Sources, below.) Spread a small amount of polishing compound (Sources, below) on the surface, and polish the finish with the polishing pad and a random-orbit sander using slow, overlapping passes, shown in photo below. Work slowly and stop when it reaches an even sheen. Then apply a coat of paste wax.
Fix 3: Add fresh topcoats
Badly scratched and dented wood can't be repaired without sanding down to bare wood. But in lightly scratched wood, you can achieve a finish that looks aged, rather than abused, by adding topcoats and then sanding those down for an even sheen and smoother surface. Use satin or semi-gloss topcoats on less-than-flawless surfaces. A high-gloss finish requires more polishing, and that gloss highlights surface flaws.
Begin with a thorough cleaning with waterless soap followed by mineral spirits to remove grime, wax, and furniture polish, which can produce fish-eye in the new topcoats, shown in photo below. Then hand-sand the surface to 320 grit to prepare it for the new coats.
A little dab will do it
To minimize small scratches that go down to bare wood, dab a matching stain on the damaged, shown in photo below, and allow it to dry for at least 24 hours. Then apply three coats of wipe-on film finish such as Watco Wipe-On Poly, sanding with 320 grit between coats.
Sanding reveals finish layers
If minor dings and missing finish telegraph up through the added topcoats, sand them with 320 grit until you achieve a flat surface. This may produce "ghosting" on the surface from partially sanding through a layer, shown in photo below, but you'll cover that with additional topcoats. Then set aside the project for at least a week in a well-ventilated area while the finish cures completely. It's ready to rub out when you no longer smell solvent fumes at the surface.
To rub out the finish, first spread a small amount of mineral oil on the surface and hand-sand with 400- and 600-grit wet/dry abrasive to level the surface. Check abrasive sheets frequently to make sure they're not clogged with clumps of finish. Wipe the surface clean with mineral spirits after each grit. Follow the sanding by buffing with a mechanical buffer or random-orbit sander and white non-woven cleaning pad. (See Sources below.) Then polish the surface using a polishing compound and soft cloth on a buffer. Stop when you achieve an even sheen.
White non-woven cleaning pads: Package of 10, ptreeusa.com.
Polishing compound: 3M Finesse-It II Machine Polish, Amazon.com.
Adhesive strips: U-Glu 1x3" strips, for eight, Amazon.com.