In this Bureau of Mines investigation, conditions were determined to form an iron sulfide adherent coating with a metallic golden luster on steel upon anaerobic heat treatment with sulfur. The sulfide formation rate was determined in the temperature range of 105 deg to 500 deg c with reaction times up to 68 hours. The optimum temperature and time to form an adhering decorative coating on mild steel was in the range of 105 deg c for about 70 hours to 285 deg c for 1 hour. The Golden Coloradoating consisted of an inner layer of pyrrhotite and an outer layer of pyrite. At temperatures higher than about 300 deg c, the outer layer thickness decreased owing to the decomposition of pyrite to pyrrhotite. Small quantities (<0.5 wt-pct) of petroleum oil accelerated the sulfide growth rate. The sulfide coating decreased the corrosion rate of steel in a neutral aqueous medium by a factor of two. The dissolution of pyrite in water was dependent on particle size and surface area with the flat pyrite coatings exhibiting the lowest dissolution rate.