Ammonia Fuming to Darken Wood

Feb 02 2018 0 Comments

Posted on January 16th, 2018 by Gaston Monge-Grassi
How to darken wood high in tannins using Ammonia:
Last year a friend of mine showed me a very old technique to darken wood high in tannins like oak for example and I was amazed by the results. It is quite cheap and easy to achieve but there are few important safety considerations:
Fuming is a dangerous process, so gear up with eye protection, respirator, and gloves. Suit up BEFORE you open the jug, or open the chamber. Try to work in a well ventilated area. Use 35% solution ammonium hydroxide, which you can get from a chemical supply. Very little is required, since a small amount will generate a good bit of fumes. One bowl will do a tented table or chair, and a 5 litres will do an entire chamber full of furniture.
Ammonia fuming is a wood finishing process that darkens wood and brings out the grain pattern. It consists of exposing the wood to fumes from a strong aqueous solution of ammonium hydroxide which reacts with the tannins in the wood. The process works best on white oak because of the high tannin content of this wood.

History of Ammonia Fuming

Ammonia fuming was apparently discovered by accident in England when oak boards stored in horse stables were found to darken considerably when being stored near the fumes from horse urine.

There are heaps of videos showing what you need and how to do this, so I chose a few for you to watch:


Here are a few points and tips I found to consider:

  • The longer the furniture is in the chamber, the darker it gets. Typical schedules go from 12 hours (a very light fuming) to 72 hours (rather dark). Test scraps first.
  • The temperature in the chamber not only affects speed of fuming, but also colour. The hotter the chamber, the more reds it brings out. Colder chambers result in a more greenish brown. Make one section of the chamber of clear plastic, and shine a heat lamp into it. Remember, ammonia corrodes aluminum, so no electrical connections should be inside the chamber. You'll notice that when the air inside gets up to 27-30 degrees, the reaction goes faster and the colours get slightly redder.
  • A simple chamber can be nothing more than a frame draped with clear or black 2 mm plastic. Make the frame of wood scraps or plastic pipe -- anything that will hold up plastic and surround the piece you are fuming. Seal the plastic at the bottom with duct tape. (Obviously, don't fume on a wood floor -- fuming works even through most finishes.) Close it and seal up the edges and seams with duct tape.

There is also a new twist to fuming I found from Mac Simmons, a veteran of the furniture finishing, refinishing and restoration trades. 

"Being rushed for time inadvertently leads to the discovery of a new technique.

Desperation Produces a New Technique

I wrote about fuming in the September 2006 issue of CWB, describing the standard process and some alternatives that can be used to achieve a similar look. But, I recently was doing a photo shoot where I needed some fumed samples in a hurry and inadvertently discovered another technique that I want to share here.

I began in the usual way: After setting up a small plastic bag as the tent and placing some pieces of wood inside, I filled two plastic containers with ammonia, sealed the tent and waited for the wood to fume. During the early evening and throughout the night, the weather got cold. So in the morning, when I went to check inside the tent, there was very little change in color.

I brought the tent into my garage and opened it up. I needed the photos right away, so out of desperation I took a sample piece of wood and brushed on some ammonia and saw that it actually colored the wood. I brushed on more ammonia, and the color got more intense. I let it thoroughly dry and then sprayed it with clear lacquer. I was very surprised at the results, as it had a nicely fumed color. I then started playing around and found out that I could lighten or darken the colors by adjusting the amount of water that I added to the ammonia.

This turned out to be a unique coloring technique, and I was excited about these findings. Also, I now had another interesting subject to write about. I “went wild,” testing some small samples of wood to see what colors I could produce. I realized that this process is so simple that all I have to do is show or tell someone what I did, and then all they have to do is some tests on different pieces of wood. They would have an easy way to get the look of fumed wood and a new way to stain wood to get different colours."


Have a great long weekend and if you have a go with this technique remember to always work in a well-ventilated area and wear personal protective gear whenever you work with ammonia. 






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