By far the most common finish used when one wants to see the grain of the wood is varnish. While there are other finishes available, varnish has been used literally for centuries. Some modern varnishes are adaptations on the original, but they still qualify as being varnish. Many of these are labeled as polyurethane varnish rather than just saying varnish.
To understand the differences that these new varnishes provide, we need to have a basic understanding of the chemistry behind varnish. There are three basic ingredients in any varnish: resin, oil and a solvent. The solvent is there to allow the varnish to be brushed on and flow, with the intent that it dissolves. Therefore, it really isnt all that important. I think we can all trust that the manufacturers will use a solvent that will accomplish the purpose.
It is the other two ingredients; resin and oil that make the difference in varnishes. The types of these ingredients used, as well as the ratio between the two of them, are what give each varnish its particular characteristics.
There are three types of resins used: phenolic, alkyd and polyurethane. In recent times, most varnishes are polyurethane, due to its lower cost, higher scratch resistance and clear coloration. The best (and most expensive) varnishes are made using phenolic. It is also possible that a combination of these resins will be used in one varnish.
There are two types of oils used in varnish: tung oil and linseed oil. Of the two, linseed oil is by far the more common, due to its lower price. However, many people feel that tung oil is a superior product, and it is found in the higher priced varnishes.
The other major distinction to look for in a varnish is the use that it is created for. Most varnish is created for indoor use, where the wood and the varnish on it are protected from weather and ultra-violet light. Spar varnish, sometimes referred to as marine varnish is created specifically for outdoor use. Since any wood left outdoors is much more susceptible to absorbing moisture and expanding, these varnishes have a higher ratio of oil to resin, making them more flexible. They also have UV inhibitors added to the varnish to protect it.
When selecting a varnish, it is important to consider the application; specifically, where the finished item will be used. If it is going to be used outdoors, then you definitely want a spar varnish. If it is going to be used indoors, then the next question is whether it will be subject to a lot of wear. A table top needs a more durable finish than baseboard and casing. Therefore, selecting a hard varnish, with good scratch resistance is important.
Epifanes is considered by many to be the best varnish around. This is a spar varnish, made from the best possible ingredients, to provide the best possible results. Read Full Review
Epifanes is considered by many to be the best varnish around. This is a spar varnish, with UV inhibitors built in. It is made with a combination of phenol and alkyd resins for superior protection. They also use tung oil, rather than the less expensive linseed oil. The best of everything is used in this varnish, to provide the best possible end result. Epifanes also has a number of other varnish products, including one that provides a hand-rubbed appearance.
As a spar varnish, McCloskey's is UV protected for outdoor use. It has the flexibility needed to expand and contract as the wood reacts to the changes in the moisture in the air. Read Full Review
McCloskey is actually an owned brand of Valspar, who bought them out many years ago. This is another spar varnish, designed for use outdoors. As such, it has the necessary UV protection and flexibility needed to survive the harshness of the outdoor environment. This varnish is made from tung oil, although the manufacturers information doesnt say what type of resin they are using. The only thing were sure of is that it isnt a polyurethane. It adheres extremely well to oily woods, such as mahogany. Available in both satin and gloss finishes.
Specifically formulated for tabletops, this urethane varnish from Behlen lives up to its name. The varnish is extremely good at resisting scratches and scrapes, as well as stains from liquids. Read Full Review
Rockhard is a varnish specifically formulated for use on tabletops and other surfaces which are likely to receive lots of rubbing. It is very hard, being made of urethane resin, so it resists scratching well. It also resists the damaging effects of water, alcohol, foods, chemicals and detergents. This is an indoor varnish that is not UV protected for outdoor use. Being a hard varnish, its not flexible enough for use where changes in humidity would affect it. The low VOC formulation is great for working indoors. Available in both gloss and satin finishes.
Cabot's varnish is another spar varnish, designed for outdoor use. It's lower cost than the other spar varnishes we've included on this list, but still provides the flexibility and UV resistance needed for exterior use. Read Full Review
Cabot makes another spar varnish, at a lower price than the Epifanes varnish listed above. This one uses alkyd resin. The manufacturer doesnt mention what type of oil is used in their literature, but based upon the price, Id say its probably linseed oil. Nevertheless, this varnish provides an excellent finish for both indoor and outdoor uses. It is UV protected, and being a spar varnish it is designed to be flexible and handle the effects of weather. It is also available in gloss and semi-gloss.
There's a reason why Minwax's products are so popular, they're affordable, easy to use, and work well. This polyurethane varnish is excellent for indoor use on furniture and trim. Read Full Review
We couldn't put this list together without mentioning Minwax, the biggest name in varnish and stains. While they dont produce a spar varnish, they do produce excellent polyurethane varnishes at a reasonable cost. This is an indoor varnish, designed to provide superior scratch resistance. However, it doesn't work as an exterior varnish, as it is not designed for that. Minwax calls this a fast drying varnish, saying that it can be recoated in four to six hours. However, many other varnishes can be recoated in the same time, so take that name with a grain of salt.