I used my electric tjanting needle to apply wax to some cruets as a resist before using glass etching cream. The wax produced nice crisp lines regardless of surface curvature:
Some of its sister cruets had finer lines in the design, but I gave those away before I had even heard of Craftster.
One plus of this method was that it went rather quickly. One minus was that erasing mistaken lines without starting over was not that much of an option.
When I ran the whole thing under cold water to get off the cream, some of the wax flaked off nicely at the same time (had to put a screen in the drain to avoid clogs). The rest of the wax had to be scraped off with a plastic knife, if memory serves - this was all a few years ago.
Dharma Trading (where I got my tjanting needle) sold me a rheostat at the same time - so you can regulate the wax heat and keep it from bursting into flames. So I guess this is another craft process that requires careful watching, but you already knew that by the time I said "glass etching cream."