Blue Rust is a wood treatment made of steel wool oxidized in vinegar.
Using Blue Rust is not the same thing as simply coloring wood. Applying the treatment on wood causes a chemical reaction that makes the material turn grey/blue to even black.
The benefit to this process is the natural origin of this reaction, when iron acetate is being brushed on the wood.
The strengths of the coloring depends on the tannin content of the wood and the state of oxidized steel in the vinegar.
The other advantage is the way you can apply it. This liquid solution can be put on against the grain to play with the wood’s nature.
Oak is strong, rot-resistant, and has all the most suitable qualities for flooring. It has a high content of tannin, which makes it the best applicant for Blue Rust.
Stockholm Furniture & Light Fair 2015