Bronze wool is a bundle of very fine bronze filaments, used in finishing and repair work to polish wood or metal objects. Bronze wool is similar to steel wool, but is used in its place to avoid some problems associated with broken filaments: steel rusts quickly, especially in a marine environment. Furthermore, steel is magnetic and can affect the operation of marine equipment, such as a compass. Steel can also discolor some materials, such as oak. This discoloration results from a reaction between the tannates in the oak and the iron in the steel, forming iron tannate, a black compound.