Copperplate Intaglio
Featured plate: "Fig 30. Irish Hound" from a naturalist companion
Run your thumb across the margins. You can feel the ridge where heavy boxwood and copper met wet rag paper. Engravers carved backwards directly into metal. One slip ruined a month of labor. The ink sits raised on the surface, sharp enough to snag a fingernail two hundred years later.
How to tell in person
Look along the edges for the plate mark. A modern photo reproduction is flat. An original copper strike has an undeniable indented rectangular ditch stamped into the paper.