Dyes won't solve all wood coloring problems but they do address most; and, they add color while maintaining clarity..
The Transparent Alternative to Pigment Stains
This article will examine the versatility and ease of use of dyes for coloring wood. We will consider the advantages of dye over pigment stains and we will highlight some important distinctions between these two colorants. Hopefully these distinctions will help avoid confusion as we move forward. Perhaps the most important distinction is found in the way dyes color wood relative to how color is achieved with pigment stains. Dyes are soluble chemicals that, depending on the type of dye, are dissolved in water, alcohol, or petroleum distillates (oil). When applied to wood, liquid dyes exhibit chemical affinity for the wood. Chemical affinity is the electronic property of a chemical by which dissimilar chemical species (wood cellulose and liquid dye in this case) are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of a compound to combine by chemical reaction with compounds of unlike composition, again liquid dye and wood cellulose. This property of wood dyes result in the dye being absorbed by and reacting with the cell structure of wood at the molecular level thereby actually changing the color of the wood.
As wood finishers, when we color wood we are interested in altering reflected light in the visible spectrum. Since both dye and stain accomplish this objective, why should one be preferred over the other? There are several answers to this question and we will examine them in the course of this article. But perhaps the most important reason to select dye over stain is revealed by the way in which the wavelength absorption properties of the wood are altered by these two coloring options. When dye is applied to wood the reflective properties of the wood itself are altered at the molecular level as the dye combines chemically with the cells of the wood. The reflective properties of the wood are actually changes. There is no opaque film of insoluble pigment on the surface of the wood nor is there a binder (coat of finish) producing a film on the surface of the wood. The result is that the actual color of the wood is changed with no diminution of figure or loss of subtle grain detail. By comparison, stain has no impact on the wood; instead it alters wavelength absorption of the exposed surface of the wood by laying down an opaque film of pigment between the surface of the wood and the eye of the viewer. In other words, wavelength absorption takes place within the opaque film of pigment applied to the surface of the wood, not within the wood. The color the viewer sees is not the altered color of the wood; it is the color of the film of opaque pigment on the surface of the wood. Depending on the stain used, this opaque pigment film can dramatically diminish the clarity of the grain and figure of the wood. The more pigment that is applied the more the subtle features of grain and figured are diminished.
What’s in a name?
Given the very different way in which dyes and stains color wood, it would seem apparent that any naming convention that equates the two would be misleading. While I have no expectation that the naming convention used in this article will be widely adopted, I will refer to these colorants as follow:
Dyes are classified on the basis of the solvent in which they are best dissolved. There are four dye types used in the coloring of wood:
So, if the manufacturers won’t give us the information we need, how are we to determining if the “stain” on our shelves contains only pigment, contains pigment and dye or contains only dye? We take advantage of what we have already learned about the properties of pigment and dye. Pigment is an insoluble solid; it does not dissolve, it does not go into solution. If left undisturbed the heavy pigment particles will settle to the bottom of the can. Dye, on the other hand, is a soluble chemical that is fully dissolved in its solvent. It will never settle to the bottom of the can, no matter how long the can sits on the shelf. Armed with this information we can easily determine what is in the can. Allow the can of “stain” to sit undisturbed for a day or two then carefully remove the lid. Insert a wooden stir stick and slowly move it across the bottom of the can, then remove the stick and observe the result.
Finally, it is not the point of this article to suggest that stains have no place in finishing wood. They do. We simply believe that dyes, and in particular water-soluble dyes, are the best and most versatile way to color wood. Stains (pigment) can be effectively used as a “glaze” to achieve special effects. These techniques are covered in other articles.
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