My partner was recently up for a big award in our LARP group, and as a fan of Brandon Sanderson had commented that it would be cool to see the physical award in steel.
Knowing that the GF couldn’t etch steel without using CerMark or similar, I decided that I would etch a resist with the GF and then use acid to do the etching. I leaned really heavily on Annie Sullivan’s tutorial as it gave me an excellent starting point. My desired end result was a shiny piece of buffed steel with a black patina. I used:
- 22g Sheet Steel
- Behr Spray Chalk Paint
- Ferric Chloride
- Acetone
- 150 grit sandpaper
- Vintaj Onyx Patina
Spoiler alert: the ferric chloride didn’t do as deep an etch as I wanted and I couldn’t get it to hold a patina. 
The sheet needed to be degreased before I could do anything with it, so I scrubbed it down with acetone and some cotton pads. After that, I used the sandpaper to prime the surface. This helped both in adhering the paint and in giving the acid something to sink into.
I sprayed on the paint and left it for around 3 hours. Enamel paint would likely stand up better to acid etching, but the chalk paint did pretty well and it dried a lot faster.
After some tests I used 1000 speed/50 power Engrave with 2 passes. I found this removed enough paint without losing fine detail in the illustrations I wanted.
The final step was to use the ferric chloride heated in a hot water bath (jar of chemical left in a bowl of hot water for a few minutes) and spread on top of the piece for 15 minutes.
Let’s just pretend I didn’t wipe some of my paint off, okay?
For anyone trying this out in the future, I’d recommend an actual etchant meant for sheet steel, but otherwise this was fun and turned out decently. Hopefully this helps someone!