1/4 cup White vinegar
1/4 tsp Salt
Fresh 9-volt battery
Electrical wire (speaker wire worked for me)
Electrical tape or other masking medium
1. Measure out exactly one gallon of water and pour into your kettle. Mark the 1 gallon mark with a temporary marker such as electrical tape. Continue pouring in 1 gallon at a time and marking each spot until you have reached capacity. In my case, the kettle goes up to 7 gallons (for you water conscious individuals perhaps you can use the leftover water to add to your fish tank, water the plants around the house or pour it into your washing machine for the next load of laundry instead of just pouring it down the sink).
2. replace temporary markers with stickers, stencils or whatever you see fit to use. I used my own desired font and size and made stickers out of them. I suggest using ultra-sticky stock for this option. Perhaps if I were to do it again I would use something that was easier to remove once the etching was complete.
Step 1: Etching the Kettle
3. Combine the 1/4 cup of vinegar (any should work but I used white) and your 1/4 tsp of salt (completely dissolved).
4. Attach your 9V battery to the kettle (+positive lead).
5. Strip the end of the negative wire and tightly twist-tie it around the end of your q-tip. Attach the other end to the negative side. I used electrical tape and a fat rubber band to help make the connections.
6. Safety Tip: DO NOT INHALE THE FUMES FROM ETCHING. I have read they are very carcinogenic. I could be wrong, but it's not worth the risk so DON'T breathe the smoke that comes from the reaction. Etching in a well ventilated area is strongly recommended.
Dip the q-tip into the vinegar solution, take a deep breath, let it out, relax, and be patient. This will take a little time. Dab the tip of the q-tip where you want to etch. If everything is connected properly and your battery has a good charge, you should see some bubbling coming from the wire portion attached to the q-tip as well as a faint wisp of smoke (that is purportedly VERY bad for you!). After going over each number three or four times I still felt like it wasn't etching very well so I left the kettle out overnight and didn't rinse it until morning. I was very pleased with the final result.
Step 2: The Finished Product
Here is the finished job. Never mind the browned portion at the bottom. That was from a previous brew that darkened the metal.
Edit: After brewing a batch of beer I plan on adding half-gallon marks and suggest it to all you brewmasters out there.
Step 3: The Etched Kettle in Action
Here's a picture of the newly-etched kettle in action.