I did this while attending the class "The Art of Spanish Colonial Repujado or Tin Embossing," taught by Maria Natividad. It was a lot of fun!
This was made on a sheet of aluminum with the embossing technique. A mold was not used for this but instead we created our own designs and used a sharp stick for making the lines and a blender stick for making the embossed 'popped out' areas. The black areas (called 'antiquing') were added by my instructor, Mrs. Natividad, a well-known embossing artist where I live (she used mine for the antiquing demo, else I would've added the blacks. The way she did it was brilliant).
The Thingy I made for 's RFE Ethereal Exhibition for Steampunk City art show.
It's a hollow book box. The ribbon holds it closed. It started out as a stockboard book but I carved out the pages and covered it with paint and paper and gears and stuff. Originally, I had it set up so the gears would move if you turned them, but it damaged the cover so I wired them all down.
I've never made this sort of thing and I had no idea what anyone else was submitting so *anxiety!* but everybody I showed it to liked it and I got offers for the prototype I made for practice, so I sucked it up and sent in the finished one.