Fuming white oak

A description of the effect, and the chemical reaction that creates it. November 26, 2001

How do you fume white oak?

Forum Responses
I've never done this myself, but the method used is simple. You use concentrated ammonia. I'm not talking cleaning supplies here. You'll need to find a source for straight ammonia. You need to find a way to confine the fumes from a pan of ammonia. Some polyethylene sheeting would work fine. This needs to be sealed pretty well to allow the ammonia to do its job. You could build a small frame that will just cover your work piece and cover that with the sheeting.

During this process, ammonia gas is created as the liquid evaporates. This gas will permeate the oak and react with the tannins in it. This will cause a chemical reaction, turning the wood dark but leaving the rays "shown off best by quartersawing" a much lighter color.

This was the process used in most of the early Arts and Crafts furniture. There are some new products out there that achieve the same effect using dye stains. Good luck, and be careful. Ammonia is rather nasty to work with, so work in a well-ventilated area.

There was a good article in Fine Woodworking, issue #126, Oct 1997 on fuming. It pointed out that suitable ammonia is available at large office or printing supply stores (for blueprint copiers).

The actual chemical name you need to find is ammonium hydroxide. We use tons of it in the semiconductor industry for cleaning silicon wafers using what is called the RCA clean aka SC-1, SC-2. VWR Scientific should have it on their website or a local chemical supply store would be a likely source. It's a very strong base and is often used in industry to make basic solutions when the PH needs to be high to get a reaction to occur. Sort of the basic equivalent to sulfuric acid.

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?)

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
At this very moment I am fuming a Morris chair I just completed. I have twice fumed oak and this is what I have found. Small items do fine in a cardboard box which is taped closed. I keep a small amount (about 1 cup) of ammonia in a glass jar with a tight lid. Once the item is in the box I open the jar and set it the box. Tape the seams and let it go overnight. Need I say that the box is outside? Wonderful results. Do your final sanding first. The Morris chair is in the driveway under my old one man tent. I spread a tarp out and placed the chair on it. Then covered it with the tent and taped the tarp up the sides. I have the original look in the morning!

Comment from contributor B:
Ammonia is a gas at room temperature. When it is bubbled through water, ammonium hydroxide is formed. The standard ammonium hydroxide solution that one might order through Fisher Scientific contains 28-30% ammonia. When ammonium hydroxide is left uncovered, the ammonia gas escapes and is available to react with the tannin in white oak to darken the wood. Household "ammonia" is a much weaker solution of ammonia and water. It can also be used to fume white oak, but takes much longer to obtain a dark stain, usually several days. This can be an advantage if one wants a very fine control over the color of the finished product.

Comment from contributor C:
I built a mission style bench out of quarter sawn white oak and decided to fume it. I was unable to find a small quantity (quart or less) of full strength ammonia and bought the store brand of the household variety. I put some ammonia in a small plastic tray, placed it in the bottom of a plastic storage container, added the bench and sealed the container. After two days, some darkening was evident and after a full week, the bench was noticebly darker but was not satisfactory. I bought a gallon of SC1, put a small amount in the pan, sealed the container and let if go for 24 hours. The color was as expected and should look great with a few coats of linseed oil. I did notice that care should be taken with handling the furniture before and during fuming. A fingerprint from some residue on a finger showed up.

Comment from contributor L:
This week I fumed two bookcases of white oak. I built a tent of 4 mil builder's plastic about 8" bigger than the two cases all around and put 28% ammonia in several tuna fish cans in the tent. I left it overnight (about 17 hrs) and the color was perfect. There was some sapwood and it didn't darken at all but the variation was acceptable. A drawer of quarter sawn oak darkened uniformly and retained its character.

Comment from contributor D:
We use 10% industrial cleaning ammonia from the local variety/hardware store. We wipe it on the assembled piece and let it do its magic. The surface will only soak up so much water and therefore so much ammonia. 2-3 applications will yield a color as deep as heart walnut. The actual color – red, brown, yellow, brown, or greenish brown depends a lot on the nature of the wood.

We get consistent color if all the wood was from the same stand of timber. There is a grain raise issue that can be remedied by sanding or burnishing in an oil sealer with steel wool. Flooding the wood is quick. Make sure you leave no standing water under or on the wood to avoid warpage. Ventilation is good also. We use 3m ammonia cartridges in our full face respirator to save our eyes and lungs. A booth or outdoors is the place, or plan on shutting down your whole shop.

Comment from contributor E:
I tried Contributor D's method with household ammonia on a white oak island countertop and it came out very nice. I just had to do a little sanding to take care of the raised nap and then sealed with Monocoat. It looks like it was stained, but no color was applied. I am very pleased with the results.