Flexner on Finishing: Finishing Cherry | Popular Woodworking Magazine
 In Techniques, Wood Finishing

Some straight talk about cherry and blotching.
By Bob Flexner
Pages: 70-72

From the February 2009 issue #174
Buy this issue now

When I opened my furniture-making and restoration shop in 1976, the woods considered best for high-end furniture were walnut and mahogany. Of course, oak and maple were also used, and sometimes cherry.

Washcoats: The left side of this cherry panel was washcoated, then Minwax cherry stain was applied to both sides (there is no stain on the middle stripe). Notice that the washcoat reduced the intensity of the blotching a little but didn’t totally eliminate it.

As had been the case through the previous three centuries, cherry was still thought of as the poor man’s substitute for mahogany. The coloring is similar, but mahogany had always been considered the higher quality wood. A large part of the reason is that mahogany colors evenly and cherry blotches.

Blotching is uneven coloring caused especially by stain penetrating deeper in some areas and leaving more color when the excess stain is wiped off the surface.

Times have changed, and cherry is now the favored wood with a great many woodworkers. Mahogany is hardly even considered for use anymore, and neither is walnut very popular. But cherry still has the blotching problem and everyone wants to know how to deal with it.

Cherry doesn’t always blotch. It depends on each specific board. Both of these panels were finished with a clear finish – no stain.

The Solution Problem
Magazine editors like to please their readers, so you see lots of articles addressing the question of how to avoid blotching in cherry.

The method for reducing blotching under a stain is widely understood. Simply apply a washcoat before applying the stain. A washcoat is any finish thinned to about 10 percent solids: that is, varnish thinned with about two parts paint thinner, shellac thinned to a 3⁄4 pound cut, or lacquer thinned with about 11⁄2  parts lacquer thinner.

Once you have allowed the washcoat to dry thoroughly (especially critical when using a slow-drying varnish washcoat commonly sold as “wood conditioner”), a stain penetrates very little so blotching is reduced. Less penetration limits the darkening of the wood, however, so there’s a trade off. Staining is less effective.

But cherry blotches even without a stain. All clear finishes (even shellac, which is often promoted as an exception) blotch cherry and, of course, so does a washcoat. It seems there’s no way to totally avoid the blotching.
This hasn’t, however, stopped magazines over the years from keeping the possibility alive, hinting that there might be a secret method somewhere.

Not Always

Test for blotching: The easy way to test for blotching is to wipe the surface of unfinished cherry with a liquid. Any liquid will work, but solvents such as alcohol, mineral spirits and lacquer thinner are best because they don’t raise the grain like water does.

One of the joys of woodworking is that we get to work with so many different woods, each of which has its own special characteristics – some of which we like and some we don’t. Cherry machines very nicely and has an especially pleasant aroma, but it blotches.

At least it usually blotches. Just as with pine and birch, which are also notorious for blotching, the blotching in cherry and whether it looks nice or not depends on the particular board. Some boards blotch in a particularly ugly way. Some blotch in a beautiful way – often referred to as curly or mottled. And some don’t blotch at all.

Unfortunately, no wood supplier grades cherry (or any other wood for that matter) by its blotching characteristics (though veneers are graded for curly and mottled). Wood suppliers grade wood for the number and size of its knots.

So you have to figure out for yourself how the cherry you are using will finish. This is much easier to do with surfaced cherry than with rough lumber.

With both situations, the easiest way to see how a finish will look on the wood is to wet the wood. Wetting gives almost the same appearance as a finish does, the difference being that the wetting evaporates and a finish turns to a solid making the coloring permanent.

You can use any liquid, but non-grain-raising liquids such as mineral spirits, alcohol and lacquer thinner are usually best, especially on surfaced wood.

Recommended Posts

Start typing and press Enter to search