Corrugation
Ruled lines that crowd where the sheet turns away and open where it faces you. Nothing is shaded; the spacing does all of it.
About this pattern
Ruled shading · engraver's practice
An engraver has one mark and gets every tone out of how closely it is repeated. A round ridge seen from the front shows equal steps of its surface compressed toward the edges, so lines placed at equal steps around the curve, not at equal steps across the page, arrive at the crowding that reads as a turn away from the light.
The profile is exactly periodic, which is what lets a sheet of it join itself on all four sides.