Fumed wood refers to a wood coloring process where the wood planks are exposed to ammonia gas. The ammonia reacts with the wood tannin and changes the wood color, usually to a darker gray-brown color. Fumed wood can also be referred to as ‘smoked wood’. White oak is one of the better wood species to fume because it has a high tannin content. The art of fuming wood can be traced back to England and is considered to be an accidental discovery. It was popularized used by furniture makers in the 20th century during the Arts and Crafts movement, and is a technique still used in modern day.
The fuming process starts with unfinished wood planks or lumber that is placed in a sealed chamber with freely circulating air. Prior to sealing the chamber, ammonium hydroxide solution is then placed on the chamber floor. The ammonia can be replenished over time during a single process. The final product color will depend on the fuming time, the size of the chamber, or the amount of ammonia used. Wood oil can be used as a finishing product to bring out the fuming effect.
Unlike topical wood stains, fuming does not obscure the wood grain and does not blotch or run. However, fuming is not an exact science and different batches of the same wood species will react differently, as wood is a natural product.