Iron Acetate Solution Prepared from Steel Wool and Vinegar for Ebonizing Wood

Abstract

Abstract Woodworkers darken wood by reacting iron in solution with tannins in the wood to form blue-black phenolate complexes, a process called ebonizing. According to the literature, the darkness and color are controlled by the tannin concentration (higher, darker) and the counterion of iron (acetate, darker). Iron acetate is not readily available, so woodworkers prepare it in the woodshop by reacting steel wool and vinegar. This reaction was studied. Products were ferrous acetate Fe(CH3COO)2.4H2O (and H2) and subsequently basic iron acetate [Fe3O(C2H3O2)​6(H2O)3](CH3COO) by air oxidation, giving a red-colored solution. Both inorganic phosphate and air (O2) were required for maximal reaction rate. A volume of 85 mL of distilled white vinegar per gram of super fine (#0000) aged steel wool provided a final reaction mixture with fully dissolved steel and no precipitated products. Maximal darkening of cherry and red oak wood with minimal application of iron solution was attained by applying a 0.125 M iron acetate solution at a rate of 1 mL per 125 cm2 of wood surface. A protocol for creating and using an iron acetate ebonizing solution is described and was demonstrated to be a much-improved version of the one currently promoted in the woodworking literature.