DEALING WITH THE CHERRY BLOTCHING PROBLEMPosted on July 9th, 2012 By Bob Flexner No comments
Cherry was long thought of as the poor man’s mahogany and was used as a substitute for mahogany. But as quality mahogany has become harder to get, cherry has become increasing popular and is now widely thought of as a quality wood in its own right.
Though cherry has a beautiful color and is easy to work, it is difficult to finish nicely because of its tendency to blotch. Blotching is uneven coloring caused especially by stains, but also by just a clear finish, that leaves some areas darker than others.
Everyone wants to know how to avoid blotching in cherry, and you often see articles in magazines purporting to tell you the solution—but then let you down. The proposed solutions either don’t work well or muddy the wood so much that it doesn’t look like cherry anymore.
The desired look most woodworkers are after for cherry is the rich rust red of old cherry furniture. Isn’t there some way to get new pinkish cherry to look like that old cherry without blotching?
You’re not going to like the solution, but here it is. The only ways to get new cherry to look like old, aged, rust-red cherry (shown in the photo) are to let the new cherry reach the darker color on its own, which could take decades, or choose cherry boards that don’t have the tendency to blotch and stain them.
It’s light, especially sunlight, that causes cherry to darken. You can get a running start on the darkening by putting your sanded parts in the sunlight for a couple of days. Or you can finish the object (without stain) and put it in the sunlight. Sunlight coming through window glass will have less effect than direct sunlight outside.
In the example shown, I finished the bottom half of the cherry board and covered the right side. Then I put it outdoors in sunshine for two days. The barely visible vertical stripe in the middle is where some sunlight passed through the tape I had applied to separate the two sides.
As the cherry ages naturally, the non-blotchy areas darken and blend with the blotchy parts, reducing the contrast so the color becomes more uniform.
In my opinion, natural aging is the best and most practical way to achieve the old cherry appearance.
It’s more practical because the other way to achieve a non-blotchy rust-red coloring is to choose boards that don’t have the blotching tendency to begin with, then stain them to the color you want. Not all cherry blotches. In the comparative example shown (which wasn’t stained), the left panel blotches with a clear finish applied. The right panel doesn’t blotch.
The problem is that no mill grades boards (or veneer) for its tendency to blotch (though they do grade veneers for curly, mottle, etc.). You have to test each board separately after it has been surfaced.
You can do this by wetting the board. You will see instantly whether it is going to blotch with a clear finish or a stain and finish. 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. It’s much easier to see if a board will blotch when the test is done on surfaced cherry than on raw, unsurfaced cherry.
The publicized method
The widely publicized method for reducing blotching under a stain is to 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 ¾ pound cut, or lacquer thinned with about 1½ 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. The 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, which is just a thinned finish. You can see blotching with no stain clearly on the left panel of the two contrasted boards.
Getting the color immediately
If you are using relatively non-blotchy wood or are willing to live with the blotching, you can achieve a color very close to aged cherry immediately by using a cherry dye stain. Lockwood natural antique cherry water-soluble dye (also sold as Moser natural antique cherry) provides the most accurate color in my experience.
These dyes are available by mail order from many suppliers. But keep in mind that the color of the wood under the dye will still darken and result in a much darker coloring than you may want after a number of years.
How factories do it
If you’ve ever looked at factory-finished cherry furniture, you’ve surely noticed that it doesn’t look like old cherry. It’s usually considerably darker, sometimes so dark and opaque it’s even difficult to see that the wood is cherry. But it’s only mildly blotchy.
Cherry furniture manufacturers “solve” the blotching problem by putting most of the color on top of the wood rather than in it. Instead of using stains, they get the color with glazes and toners. Glazes are thickened stain applied in between coats of finish. Toners are the finish itself with the color (usually dye) added. Toners are always sprayed.
If a stain is used at all, it is thinned a great deal and sprayed thin on the bare wood and left to dry without wiping. This produces a more even coloring than a wet coat wiped dry. The staining is almost always followed by a glaze, toner or both.
The end result is reduced blotching because it is largely covered over. Though there’s no reason you couldn’t finish cherry in this manner yourself, the look attained, which is shown in the accompanying photo, is not what most woodworkers want.
Here’s the bottom line on cherry.
Most boards (and veneer) blotch when stained, and also when finished without a stain. There’s no way to avoid this, other than finding boards (or veneer) that don’t have the tendency.
Over time the blotching is muted as the heartwood darkens naturally to a rust-red color. If you choose, you can get to this color immediately by staining with a cherry dye stain. But in time the wood will darken further underneath the dye.
You can also add color and disguise the blotching with glazes and toners, but you can’t achieve the rich, transparent rust-red look of old cherry this way.
The only way to get the old cherry look is to finish with just a clear finish, any clear finish, and let the wood age naturally.
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