What Finish Is That Anyway?
You've discovered a great piece of furniture, but the once-shiny finish has seen better days. If you knew what the finish was, it would be easier to remedy its condition. Now, you can find out.
The furniture piece could be relatively new or very old. Either way, there's a good chance you can repair the dull and dingy look of superficial wear by renewing the existing finish. By doing that, you'll save yourself the time and trouble of stripping, then refinishing. The trick is knowing what finish was put on in the first place. To identify the type of clear film finish on a piece of furniture, you test it with solvents. (See the chart below.) To find out, just do the following.
Note: Furniture on which there are oil finishes repairs easily. Simply apply more oil finish after removing wax or furniture polish with mineral spirits or soap and water.
Start with alcohol
Apply a few drops of denatured alcohol to the furniture, as shown in the photo above. Wait a few seconds; then touch the spot with a soft-bristle brush or a cloth. Shellac, a popular finish before about 1920, will soften and turn a bit sticky. If it doesn't, it's not shellac, so move on to the next test.
No luck? Try lacquer thinner
Change your solvent to lacquer thinner, and repeat the first step by applying a few drops of it to a new spot on the surface. If after a couple of seconds the finish softens enough to almost flow, you have lacquer. (You already know it's not shellac.) But if the finish only becomes tacky, and you know that it was built in the last 20 years or so, the finish could be water-based. To be sure, test further.
Maybe you need a stronger solvent
Try touching a bit of xylene (available at hardware and paint stores) to a different part of the finish. If the test area gets gummy, you're definitely looking at a water-based finish.
What to do when nothing works
If none of these solvents dissolves the old finish, it has to be one of the reactive finishes one that cures through a chemical reaction such as varnish or polyurethane. You must thoroughly sand (scuff up) these film finishes before you can apply another coat of the same finish. Or, in cases of severe damage, you have to strip them completely off with a paint-and-varnish remover, then sand and refinish.
Once you know what finish you're facing, you can restore it in one of several ways. Which one of the following you choose depends on the result you want to achieve.
- For nicks, scratches, and small areas of damage, try reflowing the finish. A cloth dampened with denatured alcohol will reflow shellac. You'll be able to dissolve the original finish and move it around to cover minor damage, brightening the surface as you go. This also works on lacquer finishes when you use lacquer thinner as the solvent. In either case, don't be over-zealous. You could go completely through the finish.
- Cut back the damaged surface film to a more presentable layer. Do this with 0000 steel wool (or gray Scotch-Brite) or 1,000-grit or finer sandpaper, and lubricant (linseed oil) as shown below. It's much like sanding between coats when you want to build up a finish. The trouble with this method: You don't really know how thick the finish layer is, so you could cut through it to bare wood. If your option to cutting back the finish is refinishing, you might as well try it.
- Apply more of the finish type atop the old. Classify this as a thorough finish repair; and the most time-consuming of all. You want a clean, dull finish, so first remove any polish or wax with mineral spirits or soap and water. Then, proceed as if you were adding a second coat of a new finish.
Sand the existing finish with extra-fine sandpaper (400-grit or greater) or 0000 steel wool (unless you're putting on a water-based finish, then use gray Scotch-Brite rather than steel wool so you won't end up with tiny rust spots). Then, remove all dust with a tack cloth and apply another coat of finish, as shown below. It's not necessary that you match the commercial brand of original finish, only the type: shellac, lacquer, water-based, etc.