White rings--those telltale marks left behind on your furniture by a wet glass or cup--aren't as common as they used to be. The reason? Modern finishing materials used on most furniture made in the past 20 years or so are just about invulnerable to this kind of marking.
That still leaves older pieces vulnerable, however, and that's too bad because many of the pieces most vulnerable to white spots and rings are expensive antiques and heirlooms with great sentimental value.
That's why you should be especially careful whenever you try removing white rings or spots. If you get heavy-handed or use the wrong technique or materials, you can easily end up making things worse.
With that in mind, here's a good plan of attack to follow whenever you are confronted by white rings. It starts with the safest and gentlest techniques, then slowly works up through those that are more effective, but also more likely to harm sensitive finishes.
Mineral oil: Just put some on a clean cloth and rub it over the spot. Keep this up for a minute or so. Sometimes the oil does the trick, sometimes the warmth generated by your rubbing gets the job done. If not, you can try oil of camphor (a drugstore item).
If the white ring is caused by traces of moisture trapped near the surface of the finish, the above technique should displace or draw off the moisture and the spot will slowly vanish as you rub. If the blemish is deeper or caused by a slight erosion of the surface, such as by alcohol eating into shellac, polishing may be called for.
Polishing: One of the standard folk remedies for getting rid of a white ring is a mixture of oil and cigar ashes. This is really nothing more than a slurry of very fine abrasives. If you don't smoke cigars, you can accomplish the same thing by using a mixture of oil and rottenstone, a very fine abrasive sold at good paint stores.
Another fine abrasive is automotive rubbing compound. It is sold in cans at auto parts shops or in the auto section of discount department stores. Just put a dab of this on a clean cloth and rub it over the blemish, working with the grain.
This should polish out the blemish. As an unfortunate side effect, however, that spot will have a higher sheen than the rest of the piece--something you may want to remedy by polishing the entire piece.
If the blemish goes very deep into the finish, you may have to bring out the big guns. In this case, that's very fine steel wool (grade 0000), lubricated with linseed oil. This is a pretty harsh treatment, however. If you overdo things, there's a good chance you may penetrate the finish to bare wood.
So go slowly. And be aware that this treatment will almost certainly create a spot with a heavy sheen that doesn't match the rest of your piece. You'll then have to steel wool the rest of the top to even things out. Then, if that creates a finish too dull for your taste, follow up with automotive rubbing compound, buffing the piece to the desired luster.
For these reasons, think twice before you get out the steel wool. If the stain is that bad, it might be a better idea to have a professional take a look at it. Or you might simply try hiding the blemish by going over it with a permanent felt-tip marking pen.
Art stores sell these in a wide range of colors. Get two or three that most closely match the color of your piece and, blending them if necessary, go over the blemish with very light stippling. If you don't like the result, wipe it off quickly with a clean rag dipped in paint thinner (not paint remover!).
If none of the above works, your best bet might be to cover the blemish with a lamp, centerpiece, ashtray or candy dish.