Fuming Tips and Tricks

Fuming to bleach wood is more art than science. August 29, 2005

Question
We are fuming oak components in different size polythene tents because of the different size components with Ammonia.880 which is 35% concentration. We are having trouble with consistency. Does anyone have any suggestions?

Forum Responses
(Cabinetmaking Forum)
From contributor R:
Inconsistency is common. We use anhydrous ammonia in 100 lb tanks. Humidity seems to speed up the process. Also, read heat affects it as well. We do beams, timbers and flooring all the time.

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From contributor T:
I've fumed a few pieces over the years. Yes, temperature did seem to make a difference. I used a higher concentration of ammonia than you're using. Contributor R is using NH3, which is about 82%. Can you find a higher percent ammonia concentrate? I had inconsistency, and if I was more careful on the front end and chose color-match more carefully it was much better.

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From contributor M:
I've been studying and experimenting with the original arts and crafts finishing techniques for the last five years for a book I'm writing on the subject. Your inconsistency is likely to be due to the wood you are using. A board from different parts of a log can fume differently. Boards from different trees obviously can fume differently as well. There are two ways to gain consistency. One way is to pre-coat the boards/cabinets, with either tannic acid or pyrogallic acid, or a combo of both.

I typically use .5 to 1 oz per gallon of water. Your mileage may vary. You can get pyrogallic acid from photo suppliers and tannic from Rus Ramirez's Woodfinishingsupplies.com. Look under his conservation tab.

The pre-coating technique is one of the deep dark secrets that is never mentioned in the contemporary articles on fuming. That's the way they did it back in the old days, and it works, though not always perfectly. The acids and combos of them in various proportions will also change the color you get after fuming. The other way is to blend the color with either pigments or dyes, as you would when trying to blend colors on any other woods.