[Ron Wood]

ViggoG,
The cratering that is evident in the marking is due largely to the rust blue process. When carding off the rust, smooth surfaces only exhibit mild, almost imperceptible, roughness. That is what gives rust blueing its "satin" appearance. In markings, the carding does not get down into the recesses, thereby leaving a much more textured finish. Look at any original rust blued Luger and with a magnifier observe the bottom of serial numbers, crests, etc. and you will see that they display this type of texture. You can see on the high points of the Swiss crest that they are much more shiny and smooth than the recesses.