Most likely from the platinum deposition filling in any irregularities. There are a whole series of posts here called "Eye Test" for many different blades. There are also SEM images online that we are not allowed to link to.With a magnifier lense (15x), which has two cold white 5mm LEDs attached, I took a look at the edge of some unused blades. Then I slowly tilted the blades until the light from the LEDs were reflected by the outer most part of the edge (where "it cuts"...) into the lens. It was very interesting, how different smooth these edges where.