Toward Ecosophy

He probably traced it from the grimoire using onionskin paper, which is thin enough that you can see through it. Then he blackened the back side of the paper with charcoal or some other easily transferable pigment, placed it on the piece of tin, and traced over the lines with a hard pencil or round-tipped stylus to transfer the lines. That was standard practice in the pre-photocopy days -- I did it myself when I was young.