Ink/pen dynamics and the rhythms of writing

[pfeaster]

I think it could also be that they wrote [checKhey c], recharged the pen, then added the plume of S and went on with [heol]. The leftmost c-stroke of Sheol is as faded as the final stroke of -y in checKhey, but the 'h' of Sheol is considerably darker (though less dark than the plume).

That's a fair observation, and that sequence would make more intuitive sense.  It's also true that [ch] generally seems to have been written as [c] first, with [h] added afterwards, which is likely to have happened here too.

My suspicion that the plume on the [S] was written during the same "charge" (is there a better term?) as [qokedy.ykeedy....] rests on a subjective impression that the ink in both cases is conspicuously darker than the ink anywhere nearby on the page -- so much so that it stands out visually at a higher zoom level.  This doesn't seem due solely to the sheer quantity of ink; to either side, we can see cases where a lot of ink was present but spread outward, and the overall color ended up somewhat paler after the ink dried (the [l] in [ldy] is a prime example).  Here the ink instead seems (briefly) to be more concentrated, with more color suspended in less liquid (or else liquid that didn't pool outward for some reason).  I don't know what could cause that.  If iron gall ink is left unstirred, does the coloring agent gradually settle (and become denser) towards the bottom of an inkwell?

Without being sure of the mechanism for this, of course I'm not in a position to rule anything out.

This looks like a retouch job, I can't think of a way these sharp changes in darkness without visible change in stroke width could have been produced in one go.

At least in the visible light scans, I don't see any sign of a separate outline under the darker text, and I'd be surprised if the retouching had been done so precisely as to leave none of the original peeking out from underneath.  I suppose the darker text could have been added at a different time, but that would have left rather a large gap beforehand, in an unexpected place in mid-paragraph.