What is Silver Black?
Silver Black, which is mixture of hydrochloric acid and tellurium, is a product that has a similar effect as liver of sulfur in that it oxidizes metal. This means that it's akin to tarnishing, only you are doing it on purpose and controlling which parts turn black and which do not. The reason why this effect is used sometimes by jewelers is to help show off details in a finished piece of jewelry. By darkening some areas of the metal, the detail is much easier to see. It is also a way to create an antique or patina effect, giving jewelry a look of being an estate piece rather than something brand new. Many jewelry suppliers such as www.riogrand.com sell this and other oxidizing products.
To use Silver Black, cover your work area with an old towel, have some paper towels nearby, and set out a small bowl of water and a sponge for application purposes.
Make sure you are working in a well-ventilated area. This is a toxic chemical, so you want to make sure your children or animals can't be exposed and that you aren't breathing in the fumes.
Select Your Jewelry Items
Now you need to determine what you'd like to oxidize. To give you an idea of how dark the metal can get, here is a wire, chain, and crystal double strand bracelet/choker I made. This is how it looked before I dipped it in the chemical.
This is what it looked like after I used Silver Black. I literally dunked the chain down into the bottle, and then dunked it down into the water, and dried is off with a paper towel.
Control the Darkness of Metal
If you don't want all of your piece to be black, then you need to control the amount of Silver Black used as well as the places you apply it. Pictured is a sterling charm that I didn't want totally black, just oxidized enough to show more detail. At this stage, it is highly polished.
Applying with a Sponge
One way to control how much and where you oxidize it to use a sponge (like the small makeup sponge pictured) or a cotton tip or cotton ball to dab the chemical onto the metal.
Polish Some Areas
Here is the same charm after I oxidized it and then also polished some of it off. I used a flexible shaft and polishing attachment to polish the charm. I was careful to just polish the surface and not try to polish the grooves. This way the lines or grooves in the charm have some black in them, and this black color helps the details stand out.
Unless you want your piece to be completely black, you will need to polish it some afterwards. You can use a flexible shaft like I did, use a polishing cloth, or try any number of other polishing methods. But,the idea is to just get some of it off, not all of it, so the details pop out.