He’s come up with a way of creating PCBs with any 3D printer and steel rod ... is using the traditional method of etching away copper, just some ferric chloride and a bit of time.

ferric chloride, 2 ml. concentrated hydrochloric acid and 99 ml. methyl alcohol) etching for 20–60 min ... made upon a carburized plain carbon steel, upon a carburized ‘Westinghouse Puron ...

The chemistry for any etching setup is important, and in recent years the entire community has moved from ferric chloride to copper chloride for a very good reason: you can recharge copper ...