This is mild steel but does it mean anything about cold rolling and maybe relate to knife steel ?

Etching chemically removes selective material depending on the etchant. Example, ferrite may be etched away selectively around the carbides. The result is a three dimensional plane rather than the flat plane and what you see is contrast between different phases as the light is reflected differently between the high spots and low spots.

 

Thanks, I guess this thread was total nonsense I don't know if maybe I breathed in too much metal dust cause my brain shouldn't be able to trick me like that.