Good question. The steps are grooves in the metal, of course. Maybe these grooves only direct the light in mostly one direction, unlike the rest of the coin, which scatters it everywhere.
Here is a really nice Lincoln set that I couldn't pass up. Medals are from left to right (obverse), Copper, Pewter, Sterling Silver. Click on images to enlarge. Z
Good luck! 1963 was not a good year for Lincoln production at either mint. I'm sure you're discovering that!