Color and Color Theory—Web Page

by Amy Linstrom and Jeff Schwartz

 

The Color of Materials: Wood

 

Wood is a natural and diverse material commonly used in construction framing and finishing as well as in furniture-making, sculpting, and sometimes as a "canvas" for painting. The structure and properties of wood will impact how they absorb stains and some paints and host paints, enamels, surface shellacs and sealers.

This discussion will briefly review the following:

 

Structure and Properties of Wood

Prof. Paulo JM Montiero of UC Berkeley has extensively studied and catalogued the structure and properties of wood. In addition to the broad categories of hard and soft woods (see wood types below), he notes the following characteristics of wood:

    1. cellulose
    2. a linear polymer crystalline in nature (40% to 50%)
    3. hemicellulose lignin.

 

Water may be held by wood in two ways—bound water and free water. Bound water is held within the cell walls by absorption force. Free water is situated in the cell cavities (lumin).

FSP: is the Fiber Saturation Point. This is the point at which the cell walls are saturated with bound water and there is no free water. It varies from species to species but averages about 28%.

 

Types of Wood

There are hundreds of wood types, and Different woods have different hues or ranges of color in their natural state. Any color stain, which is applied to wood will mix with the natural color of the wood to produce a modified hue from the original stain. All wood darkens with age over time. Sometimes, one type of wood is stained to resemble another. For example, Birch, while often finished natural, is sometimes stained to resemble mahogany, walnut, or maple.

For more information on wood types, please see section entitled "When Color Meets Wood" (scroll down).

Processes for Staining, Painting and Finishing Wood

The following information is excerpted from "Bench Woodwork" by John L. Fierer, Charles A Benett Company, Inc. Publisher:

 

Standard Finish

  1. Bleaching—only if very light finishes to be applied, otherwise may be skipped
  2. Staining—adds the desired color to wood or improves the natural color
  3. Sealing—seal the stain to prevent bleeding (running of the stain)
  4. Standard finish—A shellac, varnish or lacquer finish is applied after sealing.

 

Kinds of Stains

There are three common types of stains. Oil, water, and spirit stains, named according to the solvent used. Oil and water are the easiest to use.

  1. Oil stains come in many different colors, usually ready mixed. Oil stains can also be made by mixing ground-in-oil pigment or colored powder in a solvent. The solvent can be turpentine, linseed oil, or other light oil. Oil stains are easy to apply and have good color. Chief disadvantages are that they raise the grain and are quite expensive.
  2. Water stains are made by mixing a powder in water. Usually one ounce of powder will make a quart of water stain. Water stains are inexpensive, easy to use, give good clear colors and penetrates (soaks into the wood) very well.

 

When Color Meets Wood

In the May 1997 issue of Professional Refinishing, Allen Holste maintains that matching colors is the toughest part of the refinishing business. It often requires more time, trial and error than is allowed to get the right color. In order to save both time and money for all parties concerned, he advocates studying the basic tenets of color theory, namely the primary (red, yellow, blue), secondary (orange, green, purple), and intermediary (e.g. red-orange) colors, and then employing this doctrine into the matching process.

All of these words ring true when coloring wood, but for the novice, a knowledge of wood as a surface, or "canvas," is essential before coloring. With a myriad of species that can be colored, one color can appear to be two, three, or even a hundred others. The surface/medium must be studied before the process can begin.

Both hardwood and softwood surfaces vary in terms of how well a color will appear, but neither one nor the other is "better" as far as staining is concerned. Softwoods tend to accept color more quickly than hardwoods, but both surfaces generally stain well. (Incidentally, the terms "hard" and "soft" as they relate to wood are often misleading; e.g. balsa wood, as soft as it seems, is actually a hardwood.)

Open-grained woods such as oak and walnut tend to accept stains well, as do many of the closed-grain woods such as birch, mahogany, and alder (commonly used to build unfinished furniture). But many other elements evident in the hundreds of wood species will determine the appearance of a color. A key determining factor in the success of a color on wood is absorption: how porous the wood is. Wood types characterized as open-grained and ring-porous are typically the best woods to stain, with some exceptions (e.g. ash, which is better left unstained). No matter what type of wood is being colored, either a sample or a small, hidden section should always be tested to determine the desired color before staining the larger surface.

The intended color must be considered just as crucially. The predominant color of the wood must be taken into consideration before applying a stain. If it is primarily a yellow, gray, or reddish color, a stain with this hue as its base should be used. To reach the desired tone, a secondary stain can be applied in lesser amounts than the original stain. You can manage the coloring adequately by not using more than three wood tones at a time, as this makes it difficult to control the outcome of a stain.

Certain colors can be applied to inexpensive woods to emulate the more expensive wood types. The trick is to use woods with similar grains. For example, maple can be stained to appear as cherry, poplar can be used as a substitute for white oak, and alder is often employed to imitate birch or walnut. A distressed, vintage look can be created by staining a surface and then removing the stain from selected areas, particularly edges and corners, such that a brand new, unfinished piece of furniture can become an heirloom. Color on wood can even be manipulated such that the wood resembles other materials, e.g. faux marble. This works best on closed grain woods such as pine, maple, birch, aspen, or alden.

Lightening the color of wood is a difficult process. The tendency is to want to apply a lighter color, but adding more color will actually darken, not lighten, the appearance of wood. For best results, the existing finish must be stripped, and the old color must be bleached out before applying the lighter stain. Some woods are best left uncolored. Wood types classified as "antique" look better with age, and without applied color. Yellow and sugar pine woods are usually discouraged from coloring for their uneven appearance and grain patterns. Other woods, such as alder, are not recommended for dark colors. But whenever wood is to be colored, it is always best to consult a reputable source of information to determine what color should/shouldn’t be used based on the types of wood being used.

 

How To Prevent Blotching

Some woods, such as walnut or oak, tend to color evenly. Others, such as cherry, maple, birch, or pine, are harder to manage. The reason why some woods color unevenly (known as blotching) and others don’t is widely debated. Some say that the culprit is swirled grain, while others attribute it to resin pockets that occur during kiln-drying. However, as far as the coloring of wood is concerned, all of the possible reasons for blotching are irrelevant. This must always be dealt with regardless of its cause.

Certain products on the market, or methods used while staining, can alleviate this condition (but most have limitations):

When dealing with the surfaces that tend to absorb color unevenly, the following key points must be kept in mind:

  1. Control the depth of penetration as much as possible.
  2. Remember to keep the color close to the surface.