If you like the look of antiquated jewelry, here are some products to help you get the look with your sterling silver chain, findings, etc.
Solutions such as "Black Max" will blacken a piece of silver instantly. Once it's rinsed and dried, use a small piece of fine steel wool, or a 3M pad to polish away some of the oxidization on the high parts of the piece, leaving the recessed areas of the design dark. Tumbling the piece in a rotary tumbler with steel shot will really bring back the shine on the high points, but still leave the black in the crevices. It's the contrast between the shiny and the dark that really gives a piece depth and character.
"Liver of Sulfur" is the standard, most commonly used chemical for oxidizing silver. It comes in a liquid form and a solid form (chunks), and works best if either the solution or the piece of jewelry is hot. The fabulous thing about liver of sulfur is that it can create an array of colors on your metal. If you experiment with the temperature of the solution, the temperature of your piece and the length of time you leave your piece submerged, you can come out with vivid shades of violet, peacock blue, and teal! Ultimately, though, if you leave it in long enough, you will get that deep grey/black color. Again, it will need to be rinsed and dried and polished to get the full effect.
For those of you who prefer an all-natural process, you can oxidize silver with a hard boiled egg yolk! Yes, it's true. Crumble the hard boiled egg yolk in a ziplock baggie, throw in your piece of jewelry and zip it up. After a day (or perhaps two), the sulfur in the egg yolk will darken your silver. The longer the darker. When the piece is the color you are striving for, rinse and dry.
So, that's all there is to it. . . nothing mysterious and not difficult.
By the way, all of these techniques will also work on copper.