does the corten steel stain the surrounding concrete as it rusts? - I am thinking of using corten steel as a backsplash behind my bbq that will be up against an exterior wall of the house. I am thinking of either a bluestone or concrete countertop, but am worried about staining as it rusts. Your photo is beautiful and I don't notice rust stains, but have heard it can be a problem. Any advice would be appreciated. Thank you! »