Adding to the confusion is the fact that there isn't a "best" finish. All finishes can be used on any object, and you can always find someone somewhere who'll report great results with a finish you never would have considered.
Making a decision comes down to assessing trade-offs. The five primary considerations when choosing a finish are:
- ease of application
- solvent odor
If you use these as criteria to evaluate each finish, you can determine which one is best for your project.
Oil-base polyurethane is one of the most popular finishes, largely because it provides the most durable surface of any consumer finish. But it has a strong solvent odor that can permeate your house for several days, and cleaning up brushes afterward can be difficult.
Polyurethane finishes provide excellent protection on wood surfaces, from floors to tabletops. Oil-base finishes afford the greatest protection and impart an amber tint. Water-base poly dries clear and is low odor, but it's not quite as durable as oil-base.
In addition, polyurethane has an amber tint and dries slowly. Both of these characteristics can be good or bad, depending on the results you desire. The amber color adds warmth to dark surfaces, but it gives light surfaces a distinct yellow/orange tint. Slow drying is a plus if you need time to brush a large surface, but it also allows more opportunity for dust to settle and stick. Despite its drawbacks, polyurethane's exceptional scratch-, heat- and solvent-resistance make it a compelling choice for many household projects.
If you want the benefits of polyurethane without the amber color and the solvent odor, water-base polyurethane or water-base acrylic may be the answer. Both of these finishes darken wood slightly, but neither imparts any color or has much odor. The tradeoff is in durability. Even though water-base polyurethane is made with polyurethane resin, it is still less durable than oil-base formulas.
Water-base finishes also cure rapidly (like latex paint), especially in hot, dry weather. This can be an advantage for reducing dust nibs but a disadvantage if your project is large and you can't work fast enough to feather brush strokes while the finish is still wet. Cleaning brushes is easy (even easier than with latex paint).
Shellac and lacquer
Slightly less durable than either of the water-base finishes, shellac and lacquer share some of the same characteristics because they also dry quickly. Lacquer also has a strong odor.
Shellac is a traditional finish with some unique advantages. It blocks odors and stains, and it's available in clear and amber versions. However, it does take a degree of skill to apply.
If you're refinishing old surfaces, shellac has one great advantage over all finishes: It blocks odors in the wood, such as those from smoke or animal urine, as well as finish problems caused by silicone, a very slick oil added to many furniture polishes. When it gets into the wood, it causes newly applied finishes to "fish eye," or bunch up into ridges. Shellac also dries well over resin in pine knots; many other finishes don't.
Shellac is available in clear actually a light amber) and dark amber. The dark amber is especially useful for recreating the warmth of old woodwork that was originally finished with amber shellac (called "orange" at the time).
Several wipe-on/wipe-off finishes are available in home centers, including boiled linseed oil, Danish oil, 100 percent tung oil and wiping varnish. Each is very easy to apply, with no brush marks and very few dust nibs. Wiping varnish can be built up with many coats to offer good protection for wood, but the various oil finishes can't because they dry too soft. Oil finishes are perfect if you want a natural-wood appearance, but they don't protect well against liquids.
For small projects (and even for big ones if you're willing to go to the expense), you can spray an aerosol finish. I've seen oil-base polyurethane, water-base polyurethane, shellac and lacquer available in aerosol form. The advantage of using an aerosol is eliminating brush marks. Of course, the finish itself continues to have the same drying, durability, color and odor characteristics; the aerosol is simply the delivery mechanism.
Aerosol finishes work well for small projects, and most clear finishes are available in this form.
Making your choice
There's a lot to consider when choosing a finish. For beginners, I recommend starting with oil-base polyurethane if durability is important; if not, try one of the wipe-on/wipe-off finishes. Finally, if avoiding strong solvent odors is a priority, use one of the water-base finishes. As you gain experience, you can explore other options and develop your own finishing preferences.