When we process the material in our factory, the material looks like regular black steel. Upon delivery, the steel is still like this, but over the course of a few weeks to months of outdoor placement - depending on the season - the rust layer will slowly emerge. Be aware that corten steel sheets will have a layer of oil film on them, which should be washed off in lukewarm soapy water. The sheets do not always rust at the same time, but over time they will even out and become identical. Corten steel changes its color for up to 7 years. Be patient and enjoy the process. Read more and see pictures here.