How good is your pareidolia?

[oshfdk]

The original characters were traced with strokes 0.2 to 0.5 mm wide, with precision ~0.1 mm.  That is in fact the precision with which most anyone will write or draw with any sufficiently fine pen.  Just try it.  So the retracing did not require any more precision than the original scribing did.

While this is humanly possible, I'm not sure it was practically feasible. I can barely achieve 0.15 mm precision with a very good tool and a magnifying glass for a one time job performed with extreme care. I've sharpened a pencil to leave roughly 0.15 mm wide trace and tried tracing a line over mm grid. I managed to get within ~0.15 mm precision. This wasn't easy, and trying to trace the line made a jagged line. To me personally it looks nearly impossible that someone would perform this high precision (think money forgery quality) job over hundreds of pages without leaving very obvious traces, like in the right image in my previous post.

   

One thing I think could happen, is while the ink was still wet on the page, the scribe added a touch of ink with the tip of the quill to some strokes. In this case I think it's possible that the shape of the stroke would be perfectly replicated with the liquids mixing together, while parts of the letters would remain of different darkness. But to me the simplest explanation for the variations is some oily/gooey component in the ink that would capture more dye particles and create small dark blobs, which maybe weren't even visible until the ink dried out.

But maybe you meant the second e stroke in the Sh.  Indeed that is an obvious example of retracing.

I think t and ch were likely retraced, could be some failure of the writing utensil in other letters.

Edit: with a quill there is an additional complication, one would have to match not only the position, but the width of the stroke as well. I have some limited experience with the quills (both making and writing), and I have practical understanding of how they work, I think it would have been extremely hard to pull off this kind of retouching/retracing even for a professional scribe.