Ammonia Fuming: How Smoked Oak Is Made
Deep brown to almost black, with a lively grain: smoked oak is one of the finest wood surfaces there is. Behind it lies no paint and no stain, but a traditional process: ammonia fuming. In this article you will learn where the method comes from, what happens inside the wood, which wood types are suitable and how to care for fumed wood properly.
At a glance
- Ammonia fuming darkens wood through a chemical reaction with ammonia vapour.
- Tannic acid is decisive: the more tannins a wood contains, the darker it becomes.
- Oak is the classic: fuming turns oak into what is known as smoked oak.
- The colour forms within the wood itself rather than sitting on the surface as a layer.
What is ammonia fuming?
In ammonia fuming, solid wood is placed in an airtight chamber in which ammonia vapour is released. The vapour penetrates the surface of the wood and reacts there with the wood's natural tannins. This causes the wood to darken. How much depends on the wood type, its tannin content and the duration of fuming.
Because tannins are unevenly distributed within the wood, every piece colours a little differently. The grain stands out clearly, and every fumed piece becomes one of a kind.
The origins of fuming
According to tradition, the discovery goes back to old farmhouses where people and livestock lived under one roof. The beams and furniture there were mostly made of oak. Over time, the ammonia-laden fumes from the stables darkened the oak. Once the connection was recognised, people began deliberately storing wood in stables to achieve this shade. Today the process takes place under controlled conditions in closed fuming chambers.
Which wood types are suitable for fuming?
Tannic acid as the key factor
The decisive factor for the result is the wood's tannic acid content. Only woods with sufficient tannins change colour noticeably. Oak is best suited: it reacts very strongly to ammonia, right through to an almost black shade depending on the duration. Sweet chestnut and robinia also respond well. Low-tannin woods such as maple, beech or ash, on the other hand, barely change colour.
| Wood type | Tannin content | Effect of fuming |
|---|---|---|
| Oak | High | Strong darkening, from medium brown to almost black |
| Sweet chestnut, robinia | High | Noticeable darkening |
| Maple, beech, ash | Low | Barely visible change |
The right moisture content
Moisture content also plays a role. Fresh, still-wet wood is not suitable for fuming, because the reaction can proceed unevenly and leave blotches. Fuming is therefore done on well-dried wood. You can find out more about moisture content in our article on natural wood drying.
How ammonia fuming works
- Preparing the wood: the dry wood is first cut to its final dimensions and fully sanded. Only the oiling takes place after fuming. Sanding afterwards would remove the coloured layer and leave light patches.
- Fuming chamber: the workpieces go into a well-sealed chamber in which ammonia vapour is released. The seal matters, so that no vapour escapes and the fuming proceeds evenly.
- Reaction time: depending on the colour intensity required, the wood stays in the chamber for different lengths of time. During this period the vapour reacts with the tannins and the wood darkens.
- Airing: after fuming, the wood is aired until the smell of ammonia has completely disappeared. It can then be oiled.
Important: ammonia at the concentration used for fuming is corrosive and irritates the eyes and respiratory tract. The process therefore belongs in suitable fuming chambers with protective equipment and is not something to try at home.
Smoked oak compared to stained wood
Dark oak can also be produced with a stain. The difference lies in how the colour is created:
- Fuming: the colour forms through a reaction with the wood's own tannins. The wood itself changes colour, the grain stays lively and looks natural.
- Staining: here, dyes are applied to the wood and soak into the surface. This allows many shades and a very even result.
Caring for fumed wood
- Do not sand: because the colour has penetrated the wood from the outside, sanding can reveal lighter patches.
- Oil regularly: a wood oil or an oil-wax care product refreshes colour and sheen and protects the surface.
- Clean gently: a soft, slightly damp cloth is enough. Avoid harsh cleaners.
See smoked oak for yourself
The best way to experience how smoked oak differs from natural oak is in real life. Our own smoked oak is also created by ammonia fuming. With our free wood samples you can compare smoked oak, oak and other wood types directly side by side. You can read more about the individual wood types in our article Oak, walnut, ash, beech and smoked oak compared.
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