What is "fuming"?

Explanations of the process of fuming wood for color. April 11, 2001

Q.
We have a finish spec which reads "white oak, bleached and lightly fumed". What is "fumed"?

Forum Responses
Fuming is a process where the fumes of ammonia (a gas) are used on woods that have natural tannin. The ammonia fuming depends on how much tannin is in the wood. The fuming process is used to turn the color of these woods into other shades of yellow and honey-browns. Oak, chestnut, redwood and hemlock are high in tannins. The color the wood turns will depend on the strength of the ammonia and the length of time the wood is fumed.

A word of caution: You need to be very careful using ammonia. This should be done in an outdoor tent. Before you begin, spend some time researching safe fuming.

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Why would you want to bleach and fume the same piece? One will lighten/burn and the other will darken/age.

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Bleaching and ammonia can be a dangerous combination, unless you completely neutralize the bleach with a good "washing with clear water."

You may want to try using a dye stain to achieve the color, instead of going through the bleaching and fuming process on a big job. You could make up a couple of small samples, doing a bleach, then a good water wash, allow to dry, then do a fuming in a small plastic tent (outside) to see the colors you can get from the fuming.

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It may be easier/safer to first bleach the wood and then use an NGR to replicate the look.

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I hope you're not dead yet. If you are still breathing after the above advice, fuming has several definitions in finishing. The first is as explained above. The second, to spray a "fume" coat, is a light misty spray. The third and probably the most likely is to "fume with a wire brush." Simply put, wire brushing the oak to open the grain.