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.

Historically, the favorite etchant for the home PCB manufacturer has been Ferric Chloride and is still surprisingly available at a few Radio Shacks around the US. Another chloride etchant ...

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 ...