What you see is not the old tennifer or new metal hardening process. It is the black phosphate coating. Tennifer and it's new EPA approved replacement is impregnated into the steel and is colorless. The black finish is applied on top of it, and does not effect the corrosion resistance of the slide, which still has a Rockwell harness of around 68--much harder than stainless steel, which I think is around 54. Final slide finishes have varied over the years, and I cannot explain that. I've always liked the flat black of the 90's best.