I've seen the term "dark field lighting" a few times and was wondering why its used and how you do it?
An example (by one of our members no less) http://www.flickr.com/photos/spqr_ca/5362714988/.
Edit: My go at it, based on the answer (thanks!):
Well, since you used my shot as an example, I suppose I should answer... ;)
Dark field lighting is about lighting glass, a subect that is both highly transparent and highly reflective. The idea is to catch the edges of the glass, creating form and definition without dominating highlights. To do that, you need:
Now, you can do all of that with a table lamp, a black bristol board, and two white bristol boards. The idea is that you set the light up behind the black board or gobo and place the white reflectors forward and to either side. Like so:
Excuse my quick and dirty CorelDraw example... With this set up, basically, the light reflects off the white sides and defines the glass edges while the black card prevents direct light through the glass.
For a lot more information, on this and a whole host of other lighting techniques, check out Light: Science and Magic in any book store you can get it in. It's probably one of the best books on lighting you can get and is my source for this technique.