Carbon paper?

I picked up a bubble (or boba) tea a couple of hours ago (here technically known as 波霸奶茶, which, ahem, to put it delicately, means buxom milk tea). While waiting for the goods to bubble up from behind the counter, I sat fiddling with my receipt. I was number 275. When I scratched my finger on the receipt's front surface, it left dark streaks on the paper, as if I'd used a piece of lead (or a key) to write on normal paper. One of my strongest daemons (inscitiae exterminator), or maybe it's one of my best muses (inscitiae exterminatrix), started kicking up dust, demanding more knowledge. I flipped the receipt over to scratch the back: it left no marks at all. I scratched the back very hard on the table and flipped the receipt over to its printed front:　no marks had come through that way either. Only when I scratched (lightly or hard) the printed front did I get the marks. Which got me to wondering, and then to blogging...

INSCITIA:

What accounts for these marks? And what accounts for their showing up only when I scratch the paper "head on"?

COGITATIO:

I think the paper is some cousin of carbon paper. The difference seems to be that while the latter uses carbon particles to "stain" an overlaying sheet of paper, this receipt-paper uses collapsible micro-paper fibers on the front side. The printed information on the receipt is distinct from the scratches I made, just because the former are ink, while the latter are "impression shadows" made when the micro-fibers crush together under my fingernail (sort of like being able to look through glass from above, but seeing it as basically opaque-green from the side). I envsion a tiny forest of white fibers; when you scratch them, they tubmle into a tangled mesh, and look darker from above that the treetops' tips.

But why don't they crush into marks with pressure on the back? The opposing pressure from the table would seem to crush the "trees" just like my fingernail, right?

I'm really stumped; for now all I can do is scratch my mark-free head.

RESPONSUM: