The bower-barff process was a patented method of developing a protective, aesthetically pleasing, velvety black surface on iron. The process had two essential steps: the first was the intentional production of a light layer of flash rust by exposing the iron to steam; this was followed by conversion of the rust to magnetite, which is black, by hydrogen reduction using ordinary producer gas. The method had many different applications, from utilitarian water pipes to highly decorated fire proof cast iron libraries. Hydrogen reduction as a conservation treatment was also a 19th-century development that had similar features but made no reference to bower-barffing.