We are in an age when changing or enhancing the color of wood simply means using one of the fine stains or dyes are readily available. It wasn't all that long ago that the to change or enhance the color of wood was something called Fuming. It's the same thing that mother nature uses, oxidization.
Mother nature does it naturally with oxygen, but we don't have decades to wait, so we can speed up the process with ammonia. The benefits of fuming wood is that you always get a consistent color, no need to worry about dye lots or color names on the can, and the coloring can penetrate the wood up to an eighth of an inch deep for a rich permanent coloration (not longer fuming is required for deeper wood penetration). The disadvantage is that different hues and tones are difficult to control because of differing wood types and length of fuming time and even colors withing the same woods, but we can see these with stains and dyes too.
To fume wood you only need four things, ammonia (more on this later), a plastic or glass (NOT metal) container (with a lid) for the ammonia to aerate from, and some sort of a sealed plastic tent or container in which to fume the wood.
I personally have not tried to use household ammonia which is around 3% strength and is almost always mixed with soap because it is a cleaning product, but apparently it does work, it just takes longer to get the same results. I was able to purchase some industrial strength ammonia 16% from a janitorial supply store. It is relatively inexpensive at around $20. for a gallon and will last a long long time for my simple fuming purposes.
BEFORE YOU BEGIN - SAFETY ISSUES !!!!
It is absolutely imperative that you use good quality eye protection AND you MUST use a high quality respirator, NOT simply a dust mask. Ammonia is lighter than air so it evaporates readily and inhaling it is easy no matter where you work, because of it's make up ammonia will also penetrate the eyes making them sting and burn so eye protection that seals the eyes is MOST IMPORTANT. DO NOT SKIP THE SAFETY STEP. Rubber gloves and some protect clothing are also mandatory.
It is important to take your time with this project and to know what you are doing as the ammonia is very powerful and corrosive so you need to handle with extreme caution. Ammonia fumes can cause skin irritation and burns, inhaling it is unpleasant to and even deadly in the wrong circumstances and getting any in your eyes, even the fumes is painful to blinding. I may be over-selling the safety a bit, but I would rather people to extra precautions using this concentrated product.
*** NEVER use Concentrated Ammonia Indoors ***
How Fuming Works
As already stated, the ammonia fumes will basically oxidize the wood for you and in most cases will make the wood darker. Depending on the wood, it could also change the color slightly. It is always best to experiment with the woods you are using by doing some test fuming before you dive right in a fume a specific project.
In the case of ammonia, the oxidation works on the tannin contained in the wood. All plants have some degree of tannin and some trees contain more than other. Usually hardwoods, and more so the darker colored hardwoods will contain more tanning, therefore they will more readily lent themselves to fuming.
Softwoods and light colored woods will react to fuming but in a lesser way. Just as these woods do darken naturally over time, so will they darken slightly by fuming, but don't expect anywhere the same color changes in light colored woods as what you can get with staining or dying. If you are using light colored woods, like fir or pine and you want to give them a dark look, you will be best to use a dye or a stain on them.
The first thing to do is to determine which project you want to color. Once you have selected a project you will need to make a simple tent. Clear plastic is idea because then you can see through it to watch the progress.
Since fuming actually penetrates the wood up to about an eighth of an inch, it is best to fume before you glue as fuming will not penetrate a glue or filler spot. The type of wood is not so important, but remember the ammonia is reacting with the tannin in the wood, so woods with more tannin might be a better choice (like oak).
Set up you piece to be fumed inside the tent. Place a small plastic container of ammonia inside the tent, seal the opening and let it sit for up to 24 hours. When the wood has colored to the depth you want, take your wooden piece out of the fuming tent and allow it "off gas" for another 24 hours before bringing it indoors.
Like many things in woodworking we seem to keep re-inventing things and fuming is no different. The origins of fuming date back to when humans first began housing livestock in buildings. The droppings from the animals, when left in piles on the floor would eventually create ammonia gases. Some very very observant farmers noticed that when the wood in barns (and the wood they were often using was Oak) ... it would turn color and this was the earliest form of fuming.
I can attest to the power an intensity of ammonia in barns. As a youngster growing up in a rural, farming community, helping out in barns was a pretty common event and some barns would literally take your breath away ... I remember that it wasn't so much that it was foul smelling, but that it was like a gas ... that was ammonia at work. Little did I know then I would be actively trying to replicate that scenario many decades later in my life.
Many woodworkers of the Arts and Crafts era, during the times of Gustav Stickley, Greene & Greene and others, used fuming to give the Oak they used so commonly, a darker, richer look. It was fairly quick, inexpensive way to color their wood in a consistent manner that gave the wood an even better handling capability due to the depth of color penetration that was possible.
Fuming is a great way to revive old techniques and explore new ways of applying how and where it can be best utilized.
Copyright Colin Knecht