Okay, so it's not really enameling-- it's nail polish. It is quite a bit cheaper, faster, and easier though, and yields quite excellent results in my experience.
For example, I got a set of all plain silver colored earrings cheaply (except the cherry ones). There they are in various states of completion.
I usually use 1-3 coats of color, depending on the brand of nail polish and how opaque I want the color to be. You really don't need a clear top coat unless you put glitter or something on top.
Note though that your color might come out slightly different over metal with a gold vs. silver colored finish. It's not very clear in the photographs, but my one coat of green came out significantly darker on the gold cherry leaves than on the silver turtles.
If you happen to have some plain looking jewelry, this is a great way to spruce it up. And if you mess up, it comes off with nail polish remover :)
That said, I can't guarantee that all the harsh chemicals in these products will not harm your jewelry, so please do not try this on anything valuable!