Another new month, another new crocodile mystery! What manner of thing is this? Please leave wild guesses, informed opinions, witty remarks, and so on, in the Comments section. All will be revealed later this week (or sooner, depending on how the Comments go).

UPDATE December 9: All is revealed in “Mezzotint!“
Shaded area of a print created by a mezzotint rocker? NB this is a pretty wild guess — look forward to finding out the answer!
Looks like an area of print on a woven textile – silk? Or onto a textured paper? Even the non-printed area seems to have a warp and weft.
I’m with Simran: it’s the edge of a mezzotint, with stray marks of the rocker outside the image area.
Could it be the edge of a mourning page?
At first glance I thought it was fabric, then I looked more closely and decided it was probably the edge of a mezzotint. If I’m wrong, I’m in good company.