The photo appears on page 98 of "The Mousehole Forge", and is credited to a Randy McDaniel whose anvil it is, a certain 243 pound MH. It is said to be missing (Edit; not so much "missing", more like " smoothly worn through") the rear 2/3rds. of the face plate, so Randy, a blade-smith, uses the front 1/3 for blade work. From time to time he polished it for his craft, but over time it became too polished. So, he etched the surface to rough it up a bit. This caused the grain to become visible, showing the difference in wrought iron and tool steel structure. The front 1/3 shows a much straighter and very fine grain, as opposed to the large, swirling grain of the wrought body toward the heel.
Paraphrasing Mr. Postman.