CorTen steel or weathering steel is a corrosion-resistant material. When left uncoated, it forms a protective layer (patina) on the outer surface that protects this steel material from corrosion.
You will enjoy several years of color change with your Tree Art. Black scale will eventually fade to different colors of patina. Final patina will be a deep bronze/brown. This process will take 5 to 8 years depending on environmental conditions.