A while ago, I found myself wanting a good way to make metal stamps for stamping element symbols into the various pieces of metal I have, in order to identify them when the time came to melt them into new and interesting objects. To accomplish this, I used a steel bolt and the electro-etching process to make a neat little stamp for hammering into metal. I first sanded the head of a bolt so it was flat and almost mirror-like in finish. Then, I applied masking tape and used a box cutter (along with a strong light) to painstakingly cut away the design, flipped in reverse. Since it's reversed, it will stamp out in the right direction. I then attached the bolt to my power supply's +12V and hooked another wire up to the ground terminal. I then placed the ground wire in the bottom of a dish with about 1/2" of strong salt water and put a cotton ball on top of it's exposed metal strands. I pressed the bolt head onto this lightly and waited about 10 minutes. What happens is the electricity erodes the exposed areas of the positive anode, producing iron oxide. This darkens the brine solution. After about 10 minutes of etching, I rinsed off the bolt and peeled off the tape. The places under the tape were still shiny, but the exposed areas had eroded away considerably and were deeper than the lettering, as seen above.
Finally, although it might not have been necessary, I hardened and tempered the stamp. This will prevent undue wear of the stamp, since it will undergo a lot of force throughout its life. I used a propane torch to heat the stamp head bright orange and then quickly dropped it in room-temperature water. To relieve the stresses built up by the sudden change in temperature, I tempered the stamp by heating its entirety to a blue color and then letting it cool in air. After testing on a strip of metal, I was quite pleased with the result. Honestly, I didn't think it would turn out this well.