On this website: Jacqueline Cullen there are some extremely beautiful images with dark silhouettes wearing jewelry. How could one recreate this dark room effect on pictures of objects or people that were shot in normal lighting? So to be clear: my question is "what effects should I use to make normal objects/people this dark?"
You can get most of the way there by applying a Black & White effect layer and tweaking the settings of the High Contrast Blue preset. Mask out anything you don't want affected. Then apply a level effect layer over the whole business and you should be set. Of course, starting with an appropriate source photo will make all the difference. Here's a very rough example that includes a before/after reveal: