Salt water steel etching

I bought a stainless steel bottle at my university market with meal points, and decided to try personalizing it. I wanted to engrave it with something, and I ended up running across this very nice tutorial on ‘salt-water etching’. It’s a method of etching steel using only Q-tips, salt water, a 9-volt battery, some tape, and some battery leads. Needless to say, I was intrigued.

I designed a little symbol that contains my initials G, J, and R, cut it out of some tape with an exacto knife, and stuck that to a bottle.

As you can see, the positive lead was taped to the bottle, while I held the negative onto the moistened Q-tip and applied pressure to the bottle. I had to put on some gloves because I felt like the negative lead was heating up quite a bit. Indeed, if you look closely it appears that the positive lead has actually burned a small hole through the tape above it. Youch! I was basically short-circuiting the battery through the wet Q-tip and the bottle. I should say not to try this at home, but at any rate be careful.

When it works, you hear a very faint sizzling which can easily be mistaken for friction noises between the Q-tip and the bottle. However, they continue even if the Q-tip is stationary. It also smells a bit sweet and strange. You can see small wisps of smoke coming off of the metal which the author of the tutorial posits might be ozone. The Q-tip itself accumulates first a green tint, then reddish-black deposits which are presumably bits of the metal coming off. To be honest I’m a little embarrassed at my lack of understanding in terms of what’s actually going on here. I was too excited about homemade etching to do my background research.

In any case, here’s the result! It came out nice and accurate. I was worried about the water leaking beneath the tape and fuzzing the edges, but it didn’t turn out bad at all.

I also did one with the initials H, T, and B.

 

The result is basically just a change in specularity/reflectance. Depending on the light source it is nearly invisible. It’s just a local roughening of the surface, as the smooth top layer was eaten away. I would imagine that with (stronger? longer?) etching, the design would go deeper and be more visible. It seems that I went further into the GJR bottle, so it’s more visible but looks rougher. Cool stuff! If anyone knows what the green/red material on the Q-tip is, or what I was smelling, I’d love to hear from you.