Zinc alloy is a very common and popular material for jewellery components due to its versatility and low cost. It is often referred to as 'Tibetan Silver', however - while it is now a widely accepted trade name for zinc alloys - the name is a misnomer (traditional Tibetan silver is now quite rare, and has genuine silver content, while zinc alloy will generally have none).
The alloys can contain a lot of different elements, but for health and safety it is recommended to avoid those containing lead (toxic) and nickel (common cause of allergic reactions).
Like most metals, zinc alloy can tarnish and discolour. Depending on a variety of factors (metal content, finish, exposure to certain conditions), this can happen very quickly, or take several months. To help prevent tarnish, it's best to avoid moist or wet conditions, and when not in use, store in an airtight container (a silica gel sachet can help by absorbing any moisture in the container).
A tarnished fairy pendant
The fairy pendant pictured above has visible tarnish, causing the legs and wingtip to look a much less attractive brownish-yellow tone. This is thankfully very easy to remove - my preferred method is with common household toothpaste (non-gel varieties). To clean a component, work the paste into a lather and then apply directly to the piece, you can use a soft-bristled toothbrush or similar to get into grooves, or scrub at more stubborn tarnish (please note that sometimes, if the tarnish has been left for too long, the metal will remain discoloured).
Once the component is clean, rinse thoroughly to ensure there is no paste residue, then dry.
The same pendant, after being cleaned with toothpaste
Once you're happy with the result, wash thoroughly and dry to help prevent chemical residue from affecting the metal.
Removing Black Finish
Many zinc alloy components have a black finish in order to highlight the design and give them an antiqued look. Sometimes there can be a little too much black residue, or you may simply prefer a cleaner or brighter finish for the component.
As long as the finish has been applied after the casting (and not the actual colour of the metal, as you will often find with the vintage bronze and copper components), this can also be removed with another common household item, nail polish remover (I use an acetone-based remover).
If you just want to remove the excess black finish, a cotton bud dipped in the remover and wiped over the surface will usually do the trick. This tends to leave the wash in the finer grooves so that the design remains highlighted. If you'd rather try to remove all of the finish, you will likely need to immerse and soak the component completely in the nail polish remover in order to wet and thin the black finish in the finer grooves, using a soft-bristled brush to scrub.