What is the proper finish for 18th and 19th century furniture or reproductions of this furniture? The key consideration in choosing a finish is reversibility. Can the finish be removed without damaging the wood?

With this constraint, the best finishes turn out to be shellac and lacquer (nitrocellulose for the most part, definitely not catalyzed or the misleadingly named "water-based lacquer"). And refinishing is beneficial because keeping the finish in good shape is important for the furniture to survive.

Background

Finishes deteriorate as they age. First they dull, then they begin crazing and cracking. During a long period of time, finishes deteriorate because of contact with oxygen. During a much shorter time period, bright light (especially sunlight and fluorescent light) cause deterioration.

At some point in the life of the furniture (if it is to survive), the finish will likely have to be removed and replaced to renew the protection for the wood. You want it to be possible for someone in the future to remove the finish you are applying without damaging the wood.

Most pre-20th century furniture is fairly elaborate, with carvings, turnings, moldings, fluting, etc. If you use a finish that has to be abraded to get it out of recesses, even with the aid of a paint stripper, you will inevitably damage the wood in some way. Steel wool and scrub pads can't help but scratch the wood and sandpaper will round over sharp edges, dulling the beauty of the decoration.

Shellac

Many refinishers and woodworkers argue that shellac is the only finish that should be used on antiques and reproductions because it is the finish that was used originally. That is not entirely true.

It is true that shellac was the finish used on almost all furniture made between the 1820s and the 1920s, but almost anything could have been used on furniture built before the 1820s. Examples include beeswax, linseed oil and combinations of various alcohol- or turpentine-soluble resins - rarely shellac alone.

The maker used what was available and the primitive transportation system of the time often limited availability.

In many cases, furniture that was coated originally with beeswax or linseed oil was coated over with shellac at some point in the 19th or early 20th century. This could fool people into thinking that the original finish was shellac.

Shellac meets the condition of reversibility. Using denatured alcohol or paint stripper, it's quite easy to "wash" shellac off the wood. All the finish can be removed with no scrubbing necessary.

Shellac is a great finish with a long history, but it's limited in that it's available only in gloss sheen. Satin and flat sheens are usually preferred on antiques and often on reproductions to imitate the dulling effects of aging.

Of course, you can rub shellac with an abrasive such as steel wool to create a satin or flat sheen, but the scratches produced show in reflected light and are fragile in the sense that any object dragged perpendicularly across them will leave a mark. The object, even just the back of a fingernail, levels the ridges between the scratches with almost no pressure.

Lacquer

Nitrocellulose lacquer is the other appropriate film-building finish (leaving out wax, which is also reversible, but offers very little resistance to moisture).

Lacquer didn't become available until the 1920s, so it couldn't have been used originally on 18th century or 19th century furniture. But lacquer is just as easy to "reverse" by washing with lacquer thinner or paint stripper. No abrading is necessary, so no damage is done to the wood.

Lacquer has several significant application advantages over shellac. Besides being available in satin and flat sheens, lacquer has solvents that allow it to be applied in humid weather without blushing and also sprayed onto vertical surfaces with a minimal chance of runs and sags.

Also, lacquer doesn't have a shelf life as shellac does (in both flake and liquid form) and lacquer flows out well when brushed, while shellac tends to ridge at the edges of brush strokes.

On the other hand, shellac is available in a number of colors ranging from pale-yellow to dark-orange. You can use this variety to your advantage to get the look you want. With lacquer, you have to add dye or pigment to create the various colors.

I would argue that using nitrocellulose lacquer on antiques or reproductions is just as legitimate as using shellac because the lacquer will be easy to remove in the future. In further support of lacquer, it has sheen and application advantages over shellac.

Antiques Roadshow

The second argument is to stress that refinishing is a good thing. My goal is to reverse the harmful message of PBS's "Antiques Roadshow," which is not to refinish.

Sometimes furniture survives hundreds of years with its finish in near-perfect condition. Chances are this furniture was kept in a guestroom of a house that remained in an extended family for the majority of that time. For most of its life, the furniture wasn't used, wasn't moved and, most importantly, the curtains were kept shut, protecting the finish from exposure to light.

This furniture is worth more with its original (or at least very old) finish because collectors will pay more for old finishes in good shape.

But situations like this are rare and "Antiques Roadshow" doesn't make this distinction. For the dealer/experts on the show who specialize in those few pieces of furniture that have survived in near-perfect condition, no allowance is made for furniture with badly deteriorated finishes that wouldn't have survived at all if they hadn't been refinished.

Instead of saying, as they do countless times, "This furniture is now worth 'X' dollars but would have been worth 10 times 'X' dollars if it hadn't been refinished," the dealers should be saying something like this: "This furniture has been refinished, which is good because it surely needed to be. Had it not been refinished, it probably wouldn't have survived. So even though the furniture would have been worth much more had it survived with its finish in near-perfect condition, you should be thankful that someone at some time thought enough of the furniture to put in the time and money to refinish it. Now you can enjoy it."

Bob Flexner is author of "Understanding Wood Finishing."

This article originally appeared in the May 2011 issue.