Ammonia fuming to change wood’s color is a unique finishing method still in use today.

The art of coloring woods has changed dramatically over time, from coloring with natural organic resources to using the sophisticated synthetic dyes and minuscule nonorganic colored pigments that are available today. Over the years, a variety of different chemicals have been employed, and one method that is still around today is a process that uses ammonia for fuming.

In order for the ammonia fuming method to alter the wood’s color, the wood must contain tannin (tannic acid), which is a brownish or yellowish substance found in some woods, including oak, walnut, cherry and mahogany. Usually, a plastic tent is erected or a special room is used for the fuming process, and several plastic or glass containers are used to hold the commercial ammonia inside the enclosed tent. The ammonia fumes interact with the

tannin and cause a chemical reaction that changes in the wood’s color.

With fuming, the wood’s color can turn into anything from a light tan to a dark brown or any shade in between, depending on the species and how long the wood is fumed. The ambient temperature in the tent or room and the strength of the ammonia, as well as the amount of tannin in the wood, also are important factors in determining the wood’s final color.

Another factor to consider is that the color is not always consistent in certain species of woods when they are fumed. In some cases, stains can be used to make the color of fumed wood more uniform. (Even renowned furnituremaker Gustave Stickley knew about using stains when doing commercial fuming.) Some of the unifying coloring may be done with dyes or pigmented stains, colored glazes or shading stains. In addition, once fumed woods are clearcoated with lacquers, shellacs, varnishes or any of the oil finishes, there will be a color change that will darken the wood.

Nevertheless, fuming is a unique coloring process that has its place in finishing. If you intend to try it, I strongly recommend that you do some additional research first. Another word of caution: It is essential that you wear personal protective gear whenever you do any chemical fuming.

Alternatives Achieve the Fumed Look

I personally prefer using stains to color wood to give it the “fumed” look, rather then using the potent ammonia chemical. Mixed dyes or pigmented paste colorants can produce fumed colors, and with some practice you can come very close to duplicating the various colors.

Start by making complete start-to-finish samples. Colors will shift once they are clearcoated, regardless of what clearcoat is used. Just as different woods will fume into different colors, you first want to decide on the color you want to stain your wood. I used quartersawn oak for the samples that accompany this article.

The top two sections of this sample shows the colors achieved after five and 10 hours of ammonia fuming, respectively. The lower half of the photo shows the two sections after a clearcoat is applied. There is a slight difference in color between the two sections.

These four samples show various combinations of colorants on quartersawn oak. Clockwise from top left, red colorant with a little black gives a mahogany color. The next sample features burnt umber, a reddish brown color. The next sample combines raw sienna with burnt umber to produce a yellow-brown color. The last sample is just raw sienna, which gives a warm yellowish color. All samples were coated with a few applications of an oil finish.

The photo on page 52 shows a panel that was ammonia fumed. The top section, which is a tan color, was fumed for about five hours. The bottom section is dark brown and was fumed for about 10 hours.

The lower section of the photo shows the samples after they were clearcoated with lacquer, showing the subsequent color change in both the light and dark sections. This is a good example of how clearcoating can change the final color of the finish and why I always suggest making complete samples.

Here are a few universal colors I used to make up the stained samples: Red and black produce red mahogany shades. Burnt umber or Van Dyke brown with black produce many shades of brown. Raw sienna and French ochre give shades of yellow. You can combine these colors to create a multitude of other colors as well.

I use a method I call “stain dilution,” in which I take these colorants and reduce them down with the proper solvent to different percentiles. This gives me other shades of the same color. I stain a sample of the same wood with each reduction, allow the sample to dry and clearcoat the stains. The photo at left shows an example of my stain dilution chart. An additional four photos on page 54 show other colors that can be created using various colorants.

When you make your samples, the wood must be clean, well sanded and free of dust or any residue. Making up complete samples not only allows you to remedy any problems you may encounter, but also it allows you to make sure all your finishing materials are compatible.

It may take some trial and error to get the color you want. But it is always worth the time you put into learning.

Mac Simmons is a freelance writer and 40-year veteran of the furniture finishing, refinishing and restoration trades. Questions may be directed to him in writing c/o CWB, 400 Knightsbridge Pkwy., Lincolnshire, IL 60069 or via e-mail c/o [email protected].