Don't know if this is still true today, but back in the "old days" of mostly forged irons, the grooved face was simply sandblasted to give it a rough, dull appearance. This sandblasted surface would quickly wear after hitting several balls, and would look uniformly worn over time. I don't know if this is what PING does to their irons today, but it looks like it to me. If the face was not sandblasted, you probably would not see much of anything. Hint: buy "slightly used" clubs and it won't bother you as much.