Smoked Oak Ammonia Fuming
Smoked oak is actually produced by a process known as ammonia fuming. Hence, it is sometimes also known as fumed oak, fume stained oak or even fume smoked oak. The process involves allowing the fumes from a strong ammonium hydroxide solution to circulate and permeate the wood.
The fumes then cause a chemical reaction with the tannin in the wood. This darkens the wood and is particularly noticeable in the grain which is beautifully enhanced. Interestingly, this effect is most prominent when white oak is used as it has a high tannin content. While other wood species can also be fumed, they will not darken to the same extent.
The process takes place in a large fuming chamber that can be sealed so as to be airtight. The wooden boards are then spaced out on racks so that the fumes can freely circulate around the wood. The ammonium hydroxide sits in a shallow tray on the floor of the chamber allowing it to evaporate. Depending on the length of time the wood is to be fumed for, it may need replenishing at some point.
The degree to which the wood is darkened can be controlled both by the concentration of the solution and also the duration of fuming.
There is a delightful story behind the discovery of this process. It is said that someone noticed a darkening of wood stored in a stables and correctly concluded that it was probably due to the ammonia fumes emanating from the horses urine. It's claimed this happened in England and certainly, the process became very popular with the arts and crafts movement around the turn of the last century in this country.
At one stage, the technique was employed to fume smoke the architectural wood and fittings of an entire room. This was achieved simply by sealing the room as best as possible and leaving trays of ammonia solution lying around. However, it soon became apparent that this was impractical and presented a serious health hazard. A particular risk was associated to those handling the ammonia solution without the appropriate safety equipment.
Pros and Cons
Ammonia fuming as opposed to staining is permanent and does not obscure the grain. The grain is darkened and thus highlighted with smoked oak whereas staining tends to equalise the contrast between the grain and the wood.
Fuming however, tends to be less consistent because it relies on the tannin content of the wood which can vary even across one board. This can be desirable if a certain rustic character is sought though modern techniques almost entirely mitigate this. If absolute consistency is required, then opting for a stained product may be the best option. Jordan's Wood Flooring specialise in bespoke stained wood floors.
The Ammonium Hydroxide solution used is quite strong and therefore dangerous. This is not an issue so long as operators use the correct safety equipment such as: goggles, gas masks and gloves