This is the chemical name for ammonia, but the one used for coloring wood is an intensely more concentrated strength than the product you purchase for typical household cleaning, which varies from 5 to 10 percent concentrations. Ammonium hydroxide in a 28 percent concentration—found at pool supply stores—is used in a wood-coloring process known as fuming.
This color change is achieved by placing the wood inside a container—along with small open dishes of ammonium hydroxide. The container is then tightly sealed and left undisturbed for anywhere from 12 to 24 hours while the fumes work their magic. Historically, this process has been primarily identified with coloring quartersawn white oak but it works on any wood containing tannic acid or on wood to which a solution of tannic acid has been applied.
Be sure to wash your hands before handling wood that is going to be fumed because the natural oils in your skin will leave a telltale fingerprint mark on the wood during fuming!
Now technically speaking, you can brush the ammonium hydroxide onto the wood to achieve the same effect, but it is far less of a user-friendly process because of the intensity of the fumes! Also, brushing the ammonium hydroxide onto your project leads to grain-raising issues that are not found in fuming. The beauty of fuming is that the fumes do all the work for you. However, during the fuming process the color penetrates much more deeply than with other methods. Because of this it is very difficult to undo a fumed finish.
The wood must be placed in an airtight container for the ammonia to work. So, how do you do that? “Airtight” is the critical component here because otherwise the fumes will leak out, effectively undermining the whole process.
Small projects can be placed inside a plastic storage container that you find at a hardware store or home store. The ammonia can be poured into small condiment cups available at fast-food restaurants for ketchup. Place these around the perimeter of the project. After the container’s top is snapped closed, take a roll of plastic-wrap from your kitchen drawer and wrap it several times around the perimeter of where the lid meets the container to thoroughly seal in the fumes.
Medium-sized projects require a little more ingenuity. Typically what is referred to as a fuming tent is constructed around the project. This involves constructing a frame using either 1" x 2" lumber or even PVC piping that is cut and taped together. The PVC elbow joints make this an easy process, and when you are finished fuming, you can break down the frame and store it for future use.
Brian Miller lightly fumed this quartersawn white oak office cabinetry to accent the striking medullary rays. Fuming it for a longer period would have darkened the wood. He then gave it a very light wash of potassium dichromate.
Cover this frame (with the project already inside) with painters’ plastic sheeting that is at least 2 mm thick and tape the plastic along any seams to create a tight seal. Be sure the plastic is not touching the project. You want some airflow around the top of the project.
Fill the dishes with ammonia and position them around your project, then tape the whole thing closed—making sure to tape securely where the plastic meets the floor.
Large projects can go inside a rented box truck with the door sealed shut.
Rooms—Brian has fumed interior architectural millwork made of oak, cedar and mahogany by completely sealing the windows and doors in the room with plastic and/or tape and placing ammonia dishes inside the room before sealing up the exit door. The next day, wearing a respirator and goggles, he opened up the doors and windows, and fans were brought in to blow out the fumes.
You will need non-reactive dishes, such as glass or plastic (no metal) for holding the ammonia. Small margarine containers or the condiment cups from fast-food restaurants are perfectly sized for this.
There is no mixing formula. Instead, there are four variables that determine how dark your wood will become:
You should experiment on scrap wood with how many dishes of straight ammonia are required, but bear in mind that a little ammonium hydroxide goes a long way! You must wear gloves, eye protection and a respirator mask. The key is to have everything set up and ready to go so that you can put the dishes of ammonia in the tent you’ve constructed and immediately seal it up.
The fumed samples pictured here were placed inside an ordinary plastic storage bin. Two two-ounce plastic condiment cups were filled about two-thirds of the way to the top with ammonia and placed in diagonal corners of the plastic storage bin. The bin’s top was put on and the lid was sealed with kitchen plastic wrap that was wound multiple times around the point where the lid meets the bin. It was then taped securely.
The project was left inside the container for twenty-one hours.
Half of the maple sample was treated with a basic solution of tannic acid before being placed in the bin. The treated half is significantly darker than the untreated half.
You will notice that two samples of oak were fumed, and yet one is significantly darker than the other. This is because the woods contain different amounts of tannic acid. If we had left the lighter one in the bin for longer, it may have darkened more. However, based on the amount of tannic acid in the wood, the color will eventually reach a saturation point where it will not darken further.
You can dispose of the ammonium hydroxide by placing the containers out of your way and letting the liquid evaporate.
Be sure to store the sealed container of ammonia out of the sun, because the sun will cause vapor expansion and the plastic bottle will swell. Store it lower to the ground, where the temperature is cooler. The shelf life of the ammonia is from two to three years.
If you want the bottom of the project to be fumed as well, elevate your project using painters’ pyramids or something similar.
Cherry
Mahogany
Maple
Oak 1
Oak 2
Walnut
