I was inspired by Oxynox's technique in this post: http://www.craftster.org/forum/index.php?topic=211082.0
to try using glass etching cream for the first time. I made some mistakes, but over all, I like it, and I think with a little more care and practice, results could be very nice.
I chose this very plain glass cylindrical vase that came with a flower arrangement to experiment on, because I didn't like it. I thought that if I ruined it, it would be a small loss.
Step 1: I put the paper with the design printed on it inside the vase, and traced the design with black puffy fabric paint.
I traced the same knot onto both sides of the base of the vase:
Step 2: Assemble gear, including gloves and a sponge to apply the etching cream:
Step 3: Apply etching cream:
You can see here that I didn't do the neatest job, and went outside the lines in a few places. I ended up switching to using Q-Tips for application, which was easier to control.
The instructions on the jar say to leave for 1 minute. I left the cream on for 6 minutes, and rinsed it off, and there were still little bitty clear patches inside my design. I reapplied for 6 more minutes to get full frosting. So this took around 12 times longer than the instructions on the jar suggested. I suppose this must be affected by the formulation of the glass in your object.
I washed off the cream again, and then ran hot water over the fabric paint for a minute, which makes it peel off very easily.
The Finished product!
A photo in the sunlight with some hastily picked wildflowers: