Here’s one of my favorite tricks. Wet a surface to see what it will look like with a finish applied, or to make it look better if the finish already exists and is in good shape.
If you’ve done much finishing, you’ve probably discovered this trick on your own. But just in case, here’s an explanation.
Wood, whether it’s stained or not, looks darker and richer with a finish applied. The finish soaks into the wood and gives it a “wet” look, which becomes permanent when the finish cures.
Therefore, the color you see on unfinished wood, or on wood with the finish removed due to wear, is not the same as it will be when finished. If you want to see how the wood will look with a finish, all you need to do is wet the wood with a liquid that will evaporate off.
In most cases, the best liquid to use is mineral spirits (paint thinner) because it remains on the surface long enough for you to see the effect, and it causes no harm. But there are exceptions depending on the stains and finishes involved.
Let’s consider each of the four situations you’re likely to encounter: bare wood, stained wood, finished wood and damaged wood.
The most obvious example is bare wood.
As mentioned, mineral spirits is the best liquid to use for wetting the wood, but there is an exception if you’re using a water-based finish. Mineral spirits can leave an oily residue in the wood, and this can cause some water-based finishes (depending on their composition) to fish eye – that is, bunch up into ridges – if you don’t let the wood dry out enough.
So, if you intend to apply a water-based finish, it will be safer to use faster-evaporating alcohol or acetone. You just won’t have as long to judge the color.
You shouldn’t use water unless you intend to coat the entire object. It will be difficult to sand limited areas well enough so they don’t show darker when a stain or finish is applied.
Stains go on wood wet and then dry out and become lighter. The color of the stain while still damp is the color (not necessarily the sheen) you will get when you apply a finish.
If a stain has dried and you want to see the color with a finish applied, you can wet the stained wood just as you can wet bare wood. But it’s a little trickier with a stain because you don’t want to remove any of the stain’s color.
Again, the safest liquid to use is mineral spirits, but the situations are fewer. You can use mineral spirits safely over water- and alcohol-soluble dye stains and over NGR dye stain, but you may pull up some of the color from oil- and water-based wiping stains.
For these stains (the common ones you buy in a can at a paint store), it’s best to experiment on an inconspicuous area or apply the stain to scrap wood of the same species and look at the color while the stain is still damp.
The color and depth of finished wood can usually be enhanced beyond what the finish has accomplished by wetting the surface. Because of the risk of damaging the finish, the only two liquids you should use are mineral spirits and water. Mineral spirits works better because it flows out better; water tends to bead up.
Wetting a finished surface to increase depth and richness is one of the benefits provided by furniture-care products. Furniture polishes accomplish this enhancement until they evaporate. Wax succeeds until it is worn or washed off.
Wetting a finished surface with furniture polish or applying a wax has two additional benefits:disguising superficial wear to the surface and reducing additional wear. But these benefits last only until the polish evaporates. Polishes containing silicone last much longer than polishes that don’t.
The wetting trick is most handy as an aid in deciding how best to repair damage to a finished surface. The damage may be in the finish, it may be through the finish but not through the stain, or it may be through the stain and into the wood. Wetting the damaged area tells you which.
Again, mineral spirits is the best liquid to use, but you may be at a friends or neighbors where this solvent isn’t quickly available. For these situations, the handiest liquid is saliva from your mouth, and it is what I almost always use anyway, even in my shop.
Take a little liquid on your finger and apply it to the damage. If the liquid puts all the color back in the wood, all you need to do to repair the damage is apply some finish to the area. Wipe-on finishes such as oil and wiping varnish are usually effective and easy to control.
If the liquid makes the damaged area darker but not dark enough, you’ll need to apply some stain in addition to a finish. You may also apply a colored finish – that is, finish with pigment or dye included in it. It’s common to brush this on with a small artist’s brush.
If the liquid has no effect on the color, the wood is still sealed and you’ll need to apply some colored finish to correct the damage.