A worried lady called us with the following story:
In her kitchen an Oak floor had been installed (wood-engineered) and, as can happen in areas where cooking is done, in front of the cooker splashes of grease had marked to floor. Knowing how well ammonium can cut through grease she'd used some on a cloth and rubbed away the solidified grease stain.
Only to discover a few hours later the Oak in the treated spot had turned a shade darker than the surrounding area!
Oak and Ammonium - think old cow sheds
(Image from Farming in France blog)
Oak contains tannic acid and, when exposed to ammonium, this acid reacts and becomes darker. It's natural reaction, just think of old cow-sheds, barns or old train cattle wagons.
Original Oak from any place where cattle has been for a long while is well known for its very dark colouring. Trying to sand the beams or boards bare to expose the blond wood again is very difficult to do, because years and years of being "exposed" to cattle with their wee, containing ammonium, this natural discolouration has penetrated deeply in the wood, not just stained the surface.
This natural process is still being used (in controlled and safe circumstances - SO DON'T TRY THIS AT HOME!) to produce "smoked" Oak. Mostly done in air-thight chambers in a factory, exposing untreated Oak to ammonium vapours for hours. The amount of tannic acid in the Oak, combined with more or less time in this "smoking chamber" determines the natural darkness of the boards.
Another name for this process is "fumed" Oak (from the French word fumé).
In the "olden days" some exceptional specialist floor companies did "smoke on site", using very strong ammonium in a bare room, sealing off all doors, windows etc. Any draft coming in to the room while this "not suitable for human exposure" was in process would affect the result. And nothing else in the room could be made of Oak, it would get darker too. So, once again: DON'T TRY THIS AT HOME!
Note: some wood floors are incorrectly branded - excuse the pun - as smoked or fumed and only have been treated/stained with a colour to resemble this natural effect. The way to find out is to check if the colouring is only "skin-deep" - not even 1mm in the wood - or truly in the wood, at least 1 - 2 mm deep.
No, not that easily - IF the wood floor has been maintained regularly to keep the wear and tear layer in proper condition.
The floor in question had not been maintained for a year, and because the area in front of the cooker had had the most "traffic", the protective finish was rather reduced, enabling the ammonium to react with the "bare" wood.