Hands-on finishing that machines can’t touch

28_bob_fexnerWoodworking skills in furniture factories have been largely replaced by computerized equipment, but this hasn’t happened nearly as much with decorative finishing. While the simple spraying of clear coats is often done by robots or in flat-line assemblies, coloring steps are still done largely by hand. These steps can produce quite sophisticated results and you don’t have to be a factory to take advantage of them. They work just as well in smaller shops. Some of the steps are applied directly to the wood, while others are done within the finish.

Color equalizing

The randomness of factory assembling lines typically results in mixed heartwood and sapwood — and even different species of wood — in the same object. The various colors need to be brought close or “equalized” and this is easiest to do directly on the wood.

The best way to lighten the darker parts is with a two-part bleach, but it’s usually better to go the other way and darken the lighter parts. If the wood is to be stained dark, equalizing can be accomplished fairly well with just a dye stain applied to the entire object. Equalizing is less effective when using lighter-colored dyes. It is also much less effective using stains that contain binders and pigment, such as oil, water-based and lacquer stains, because the coloring effectiveness of these stains is much less.

A more sophisticated method of equalizing is to stain just the sapwood or just the lighter-colored woods to bring them close in color to the heartwood. This is usually called “sap staining” and involves application of dye just to the sapwood, best done by spraying.

Undertone staining

Another color-enhancing step applied directly to the wood, beyond simple staining, is undertone staining. This is done after equalizing, if that is necessary, and can be used to further equalize uneven coloring. It can be done with either a dye or pigment stain.

A common example of undertoning, especially effective on mahogany, is to first apply a bright yellow dye. Then follow with a dark-brown pigment stain or, better yet, with a dark brown glaze after applying a sealer or washcoat.

Strikeout

Strikeout can be done directly on the wood at the stain level or later between coats using a glaze. It involves removing some of the color using steel wool, abrasive pad or sandpaper to accentuate the figure or even create the appearance of figure where none existed.

Think of the cathedral pattern on crotch mahogany. After applying a stain or glaze, “strikeout” some of the color in the lighter areas. This will highlight the pattern.

Filling

Sophistication is added to medium-porous woods such as mahogany, walnut and quartersawn oak by filling the pores. (Plain sawn oak is a coarse wood that I don’t think is improved with filled pores.) Filling is done using a pore filler after the wood has been colored and after a sealer or washcoat has been applied.

There are at least three reasons why it’s best to apply the pore filler over a washcoat or sealer (meaning a first coat of finish, not necessarily a special product) rather than directly over stained or unstained wood.

First, the washcoat (which is a finish or sealer thinned to about 5 percent solids) blocks the colored filler from coloring the wood overall rather than just in the pores. So better contrast is achieved. Second, removing the filler by wiping is made easier because of the slicker and harder surface. Third, adhesion with the next coat of finish (or washcoat) is improved because the two knit together incorporating the filler.

Glazing

Glazing is probably the most versatile and useful step for adding modifications to the color of the object. It is always done over a sealed (or washcoated) surface and always protected with an additional coat of finish.

The glaze product is a dispersion of pigment in a slow-setting, easy-to-wipe vehicle. The thinners, usually petroleum distillates, have a low enough solvency so they don’t bite into the underlying finish.

The glaze can therefore be manipulated (moved around or selectively wiped or brushed off) for a short time after applying with a rag, brush or spray gun.

There are a great number of effects that can be accomplished with glaze, limited only by your imagination. Here are a few:

• Adjust the overall color without significantly obscuring the wood.

• Add depth or the appearance of age by leaving more glaze in recesses.

• Accentuate the structural details of molded trim or raised-panel doors.

• Add imitation grain using special tools.

• Highlight and emphasize figure by “striking out” glaze in the areas you want to be lighter.

• Add character to otherwise plain and boring painted surfaces.

• Highlight the tops of 3-D surfaces such as carvings and turnings using a “dry-brush” technique, which involves dragging an almost dry brush over the surface.

Toning and shading

Toning usually refers to a highly-thinned finish with pigment or dye added, sprayed evenly over the entire surface to tweak the overall color. Shading usually refers to the same thinned and colored finish sprayed selectively. When shading, a dye colorant is usually best because pigment can cause a noticeable muddying on the areas sprayed.

Shading can be used to further equalize uneven coloring in the wood or to create interesting effects such as a darkening near the edges of tabletops.

Both toning and shading need to be protected with an additional coat of finish.

Pad staining

This is a highly skilled color-enhancing or color-blending technique that selectively adjusts the color by padding an NGR dye thinned with alcohol, to which a little water is added to reduce the “bite.” The pad used is similar to a traditional French-polishing pad.

Like toning and shading, and unlike glazing, pad staining is fairly irreversible if you don’t like the results. You can abrade off the added color, but doing this often makes the problem worse.

Rubbing out

Rubbing out involves first leveling the finish with sandpaper, then rubbing with finer and finer abrasives until you get the sheen and perfection you want. It’s usually done just to tabletops.

The only way to achieve a “perfect” finish, no matter what you might read or hear in marketing and editorial hype, is by rubbing out.

One more thought

The methods discussed here work best with lacquer-type finishes. Most could be done with shellac. But they are difficult to do and many adjustments would have to be made using varnish or water-based finish.

Bob Flexner is author of “Understanding Wood Finishing” and “Flexner on Finishing.” 

This article originally appeared in the March 2014 issue.

Comments (1)
1 Friday, 13 June 2014 17:34
Scott
Hi. I'm working with Brazilian Cherry and am thinking about a tung oil, or more likely, a tung oil hybrid (like Minwax)finish. I was told to not sand the project too finely (150 grit at the most) to allow the pores to absorb the finish. Then after a couple of coats, I could sand the finish to be glassy smooth with 400 or 800 grit. Does that make sense to you, or should i sand the project itself as finely as i can? - Thanks!

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