I started out by taping off the outside with painters tape, and then using stickers to mark off the letters. I was slightly leery about using stickers, but the lady at Michaels insisted they would block the etching cream. I used Armour Etching Cream for the project, and saved since we had a ton of painters tape from our house remodel readily avaialble. I put a decent layer of etching cream in the taped off area and waited the five minutes suggested on the container.
I actually waited closer to 10 before I washed off the first container. The etching cream barely showed on the glass, and I noticed some of the cream got under the letters, making them not as crisp and clear as I wanted. I added more cream to the two remaining containers and waited another 10 minutes before washing it off. The second round turned out better, but the cream still leaked under the tape in several places. I would suggest using a ton of etching cream and waiting at least 20 minutes before washing it off to make the area clear and solid. This was my final result, which I might need to redo down the road.