"Fumigated" or "fumed oak" is oak which has been darkened by exposure to ammonia vapour.
Fuming oak, a chemical process of colour change for oak furniture, comes with exposing oak to the fumes of ammonia within an airtight container. Chemically, woods with high tannin content darken by exposure to ammonia gases. (Depending on the oak's type, its tannic acid reacts, producing a particular shade.) Begun at least in the mid-19th century -- see quoted passage below -- the popularity of ammonia fuming of oak increased as the century passed into the early 20th century. (The greyish-brown colour obtained initially fades to a yellowish-brown.) Used in the so-called 'quaint style' of furniture.Ammonia fuming was also extensively used by Gustav Stickley (1857-1942) to give American white oak furniture a 'rich nut brown' shade. It was also used in factory-made furniture of the early 20th century. In many cases the fumed results were often uneven and had to be adjusted by hand colouring and finishing. In the later 20th century it has been mostly used for ecclesiastical work.@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Ammonia fuming, a process darkening oak. (Mahogany may be fumed slightly.) Pieces to be darkened are set in an air-tight box, surrounded with dishes of strong liquid ammonia. According to the length of exposure, by chemical action, the fumes make the oak light brown or rich brown. Some varieties of oak darken more readily than others, although sapwood does not fume.
While the fuming process does not raise the wood's grain, it is essential that all grease, dirt, glue, etc., are removed from the surface.
An inspection glass is an advantage. Do not lean over the container when it is open. Avoid getting the ammonia on your hands, because the fumes are powerful. While imitation fuming is obtained by wiping the wood directly with liquid ammonia, the effect is not the same as genuine fuming. After the wood is fumed, you wax or French polish it.
The appearance of Old Oak may be obtained by exposing any article of new oak to the vapours of ammonia. Every variety of tint may be obtained according to the duration and temperature of the volatile compounds. A new oak carved arm-chair exposed to the vapours of ammonia, will in about twelve hours have all the appearance of its being made 200 years since; and any other wood similarly exposed, will obtain the appearance of oak.
Source: William Laxton The Civil engineer and architect's journal, Volume 12, February 1849 page 60
The treatment of oak with fumes of ammonia in order to give it an antique appearance.
Westminster Gazette. 27 February, 1893, page 8, column 1.
To read more on the source below, Cassell's Cyclopaedia of Mechanics, click here.
Fumigating Oak and Mahogany. Articles of oak or mahogany are given an appearance of age or enriched in colour by shutting them up for a time in an air-tight cupboard or box, on the bottom of which have been placed dishes of liquor ammonia pt. is generally sufficient fora box 9 ft. long, 6 ft. high, and 3 ft. 6 in. wide. It is a good plan to have a few squares of glass inserted, through which the action of the fumes can be watched. A well-made packing case will do, with strong brown paper pasted over the joints. This process will give shades varying from light olive to deep brown. Its chief advantage is that it does not raise the grain. To test whether any kind of wood can be darkened by fumigation, take a piece freshly planed up on one side, take the stopper out of the ammonia bottle, and lay the wood over the mouth. The vapour, of course, will be strong, and if the wood can be darkened, it will very soon show a patch of altered colour. A small bit of wood will do, anything large enough to cover the bottle's mouth. On a large scale you can try by pouring some of the am. monies into a cup, and covering the top in a similar way. The woodwork must be perfectly free from grease or marks of handling. Should a case large enough to hold the wood not be procurable, a small spare-room may be made to serve the, purpose if the precaution is taken to paste paper over any openings such as the fireplace.
Fumigated oak is generally finished by wax polishing, but there is no reason beyond custom why it may not be French polished or varnished. Some kinds of oak are not susceptible to ammonia vapour. It is not always convenient to adopt fumigation when a like result can be gained by other means.
Source: Paul Noonan Hasluck, ed., Cassell's Cyclopaedia of Mechanics London: Waverly Book Co, nd. page 66.
For fuming, oak should be chosen clear of sap, as the sap always shows white ; it is only the heartwood that takes the fumes of the ammonia. Austrian wainscot takes the fumes the best, and is the best wood for carving, being clean, straight, and fine grained. American white oak takes the fumes fairly well, but red oak does not, and should not be used if it is intended to fume the work. English oak fumes nicely....
Source: Paul Noonan Hasluck, Wood carving comprising practical instructions, examples and designs ... London, Cassel & Co., Ltd., 1908, page 102.