“Fuming” is a method of coloring wood by exposing it to ammonia fumes. In short, the wood and ammonia are sealed into a fuming chamber where the concentrated fumes react with the tannin in the wood and cause it to turn anywhere from a rich brown to almost black, depending on the length of exposure. The method became popular around the turn of the century, especially with Arts and Crafts furniture makers, who liked it because it evenly colored the quarter sawn white oak they favored. The process lives on, and is still considered the method of choice for Mission style furniture. And it’s not all that difficult, although there a few important safety considerations. Below, Michael Dresdner explains the process – including how to protect yourself - in answer to a Woodworkers Journal eZine reader’s question.
Q. "Fuming wood. It's a finishing technique used in Mission style furniture. What strength ammonia is required and where to obtain it? Does it require heat and how much heat? How long does the process take, and how much ammonia is required? Does anyone have any ideas for the "Fuming Chamber"?
A. Michael Dresdner: "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. Use 35% solution ammonium hydroxide, which you can get from a chemical supply house or blueprint supplier (this is the ammonia used in blueprint machines -- something becoming increasingly rare thanks to computer plotters.) The ammonia generates fumes that are trapped in a chamber -- hence, 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 gallon will do an entire chamber full of furniture. Naturally, it can be used again and again."
"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 color. 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 80 or 82 degrees, the reaction goes faster and the colors get slightly redder."
"A simple chamber can be nothing more than a frame draped with clear or black 2 mil 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.) For a more permanent, reusable one, try one of those ubiquitous Rubbermaid storage sheds. Close it and seal up the edges and seams with duct tape."
From the Woodworker's Journal eZine Archives
You’ll also find some great tips on fuming white oak in the Woodweb Knowledge Base. As a bonus, the discussion includes a glimpse of how they did things in the old days:
"There was this old story about fuming my grandfather told about oak and some other woods done in France. He said the work was interior installations of small stores. When the work was complete, everything inside the space was removed, and all windows and doors were sealed except one. This would be sealed from the outside. When it was sealed really tight, the finisher would set a big flat pan of ammonia on a metal grate, and light a real thick candle under it. Next morning he'd come by, check the color, make sure the candle was still lit, and wait for the right tint to the wood. (Ahh… the old tricks--who would care to hand stain an entire architectural molded interior space?)"
(We assume that wood fumers of years past used appropriate, government approved safety equipment as well – of course they did. - ed.)
If you have access to the Fine Woodworking magazine archives (a modest subscription fee is required) make sure you read Kevin Rodel’s "Fuming with Ammonia” (FW # 126). You’ll find a thorough explanation of the process and a look at how fuming works with species other than the traditional white oak. Marc Spagnuolo (aka the Wood Whisperer) offered his wood fuming method recently (see May 14). Note the emphasis, again, on taking the proper safety precautions.
Finally, if you want to learn Mission furniture making from start to finish, pick up a copy of The Furniture of Gustav Stickley. It covers the entire process, including how to fume your finished projects to the point of perfect authenticity.