This was my first reticle experiment. For the "Mark I" I glued a piece of a perspex ruler over the film guide. The black lines are about 200 microns thick, so they don't vanish completely. Instead, they give an excellent example of emulsion bleeding. Note how they thin out when passing over the white car and the white panels on the truck.
This "thinning out" suggests a natural cause for covered-over hairs. If thick lines can naturally become thinner, then thin lines can vanish entirely. Thinned-out lines are unlikely to be the handiwork of "whistle-blowers". It takes more work to precisely erase the line on both sides, rather than paint over it in one swipe. Why should these guys go to more effort, at the same peril to their futures, for halfway measures?
As you might expect, thinned-out cross hairs are more common than the completely covered variety. Examples such as this one, where the reticle is greyed out by the astronaut's glove, are easy to find. It came from page 67 of Dark Moon.
