The days when you could walk into a hardware store, paint establishment or home center and buy a can of varnish that would perform exactly as it did for your father and grandfather are long since gone.
These days, varnish is a sweeping term used to describe a variety of clear finishes that may be glossy, semi-glossy, satiny or flat. They can be applied several different ways. They may be natural or synthetic and come under many names, some of which don't even hint they are some form of varnish.
One way to find your way through the labyrinth of terms is to read the brochures and other material put out by the manufacturer of a product you are interested in and see whether it is likely to fulfill your needs.
Doing that and checking the label will give you the information you require on what the product is designed to do. You then can make your decision, based on brand names you are familiar with or have heard about, your conversation with the dealer and, when it has a bearing, price.
The new polyurethane varnishes generally give a more durable finish than the varnishes made of natural resins. They cost more, but are easier to brush on, dry more quickly and have excellent clarity. Like all finishes, but even more so, they should be used according to directions.
For instance, while shellac has always been a good undercoat for regular varnish when it is diluted properly with denatured alcohol, it is not recommended by the polyurethane manufacturers, who are in most cases the same manufacturers who produce the standard varnishes.
Most clear finishes don't require shaking or stirring and, in many cases, you are warned against these actions. They are inclined to cause bubbles that affect the finish.
Satin finishes, however, should be stirred gently so the ingredients are blended well.
How do you know which kind you have? Read the label carefully. Another thing to be checked is whether your varnish is designed for the surface for which it is intended. Both natural and polyurethane varnishes are available for use indoors and out. Some are especially suitable for floors. And you must be alert to the degree of gloss the product promises and you want.
No matter what kind of varnish you get, guard against the application of it in an area where dust is present or likely to be raised. If you leave a newly finished piece of furniture in a room where people may be walking, it is likely to pick up dust. Most wood finishers vacuum the room in which they will be working to prevent dust from spoiling a new finish.
A varnish brush (it should be just that, not one that has been used for anything else) should be dipped in the container about one-third the length of the bristles.
The wet brush should not be dragged across the inside of the can to remove the excess. Instead, remove the extra varnish by tapping the brush lightly against the inside of the container or merely letting it drip.
Apply with long, light strokes in the direction of the grain, then immediately stroke against the grain. The final movement is with the tips of the bristles in the direction of the grain. It does not matter if, at this point, the bristle tips are almost dry. All three of these applications are done with light pressure.
You can buy what are called tack rags to pick up specks of dust from the newly applied finish. This also can be done with something like a toothpick. It is not written anywhere in concrete that the dust specks should be removed one way. Whichever method works, including one of your own making, is the one you should use.
Turpentine and mineral spirits are the solvents for varnish, but here again you should follow the manufacturer's directions. The container label will specify what the mix proportion is if and when the varnish must be thinned. If it doesn't, you should use one part thinner to four parts varnish.