Rings, Dents, and Surface Scratches
If you have dealt satisfactorily with the kinds of polishes to use on your furniture finishes, you may have noticed that the variety of finishes produces a variety of surface problems. Why does a damp vase of flowers make a white ring on one tabletop and a black ring on another? No self-respecting antiques buff would leave damp vases hanging about, but since guests and children do not necessarily acquire our infinite wisdom with appropriate haste, rings and surface things need to be explained.
Rings, dents, and surface scratches on your furniture are an indication that you live in a house with people in it, or that you inherited your furniture from people (as compared to, for example, museums). Anybody who has a house full of perfect furniture is either obsessive-compulsive or a Maiden Lady with no cats. One of the several charms of good hardwood furniture is that the dents and scratches eventually run together to create an antique.
You may have noticed that new commercial furniture, usually the sort with 1/28th inch veneer and pressed wood back, has a finish "distressed" with what look like tiny blobs of ink. Such markings went out, I think, with quill pens - and even on antique desks, the inkwell spilled instead of dribbled. The day may come, however, when the dents and scratches on your furniture appear to you to be damage instead of antique. In that case, there are several home solutions to several finish problems.
If you have a Townsend-Goddard desk, or one of Marie Antoinette's dressing tables, don't try a home solution, even one approved by a Cabinetmaker, as these are. You wouldn't ask your twelve-year old, just learning to cook, to prepare Thanksgiving dinner for visiting dignitaries, would you?
White water marks are the result of dampness reacting on a sealed finish such as shellac or lacquer. Varnish is its own special category: it is relatively impervious to mistreatment, unless the party was very long and the glasses aren't removed until after the hangover. If it is old and cracked, it will be pervious. (Polyurethane, of course, is at risk only from hammers and hurricanes.) Dampness gets into the finish itself, not the wood beneath, and turns it white. If the finish damage is very shallow, rubbing mayonnaise (any oil) with the grain might work. If that doesn't help, the next quickest solution is fine steel wool (0000): rub, with the grain, over and over again, until the white begins to disappear. You are, in effect, very slowly removing the finish by sanding it off. You may need to go all the way through to the wood, or you may not, depending on the depth of the water mark; tiny white dust particles, the sanded-off finish, now leaves the surface powdery-looking. Clean with turpentine and apply two or three layers of paste wax. You will be able to see the place you scrubbed, since the finish is more or less removed in that spot, but the damage is less obvious.
If you are very brave, you can replace the shallac or varnish in the spot you are repairing - if, in fact, that is the finish it is. Either ask a cabinetmaker, (he needs to see the piece to determine the finish) or buy yourself a small container each of lacquer thinner and denatured alcohol. Pick a place on the piece that has finish but doesn't show, and brush (use an artist's brush - you aren't in the refinishing business yet) a little of each of the solvents on the surface. If one of them softens the finish so that you can rub it off with a paper towel, it is shellac or lacquer: denatured alcohol is the solvent for shellac and lacquer thinner is the solvent for lacquer. If, at this point, you don't understand which solvent applies to which finish, take up needlepoint and bring the piece to the cabinetmaker.
If the finish is lacquer, abandon the whole project and wax the repaired spot. Lacquer dries so rapidly that it must be sprayed; you will have a mucky mess if you try to brush it on the damaged spot, and if you buy a spray gun you are losing ground in your battle to save money by fixing it yourself in the first place.
Most old finishes are shellac, however, so it is likely that the denatured alcohol is the proper solvent and that shellac is the proper repairing finish. Buy a very small can of white shellac at your local hardware store. Use maybe a fourth of a cup and add an equal amount of denatured alcohol; brush it (again, with an artist's brush) with the grain on the spot from which you have removed the finish. Feather it around the edges, and let it dry. Steel wool again, and brush again. Keep up this process until the damaged spot is built up to match the rest of the finish. For a final polish, steel wool the whole surface of the piece and wax it. You can use the same process to repair a varnish finish, using, of course, varnish instead of shellac. You may by now have determined that it would have been much simpler to wax the spot to start with, or to refinish the whole surface.
Black rings, since they are in the wood itself, are another set of problems to be dealt with at another time. Dents, however, can be fun; you can iron them. Please don't tell your neighbors or your mother-in-law that you iron your furniture, because most cabinetmakers get grumpy about being called as a witness at an insanity hearing, but here is how you do it: place a wet cloth on the dent and hold your iron on the cloth, allowing the steam to penetrate the wood. This works well on an oil surface, since steaming a shellac or lacquer finish will create the white water mark problem, but even that can be done if you are willing to go through the process above. The wood will swell, and the dent will either lessen or disappear, depending on the depth of the dent. Do not apply this technique to dents you have placed in the heads of family members for laughing at you while you iron your furniture, as human finishes are more difficult.
Finishes are live things, too. There is no way to describe a true patina, made from hours and years of rubbing by human hands; it needs to be felt to be understood. My husband and I have visited museums wherein I stood guard while he touched the furniture. The Metropolitan Museum in New York understands that; it is the only museum I know of which allows its furniture to be examined, hands-on, by a cabinetmaker. Carefully, of course.