Hi Linda, although an antique patina look can be added to most metals by using Liver of Sulfur (LOS), most silver-plated wire, including the kind on WireJewelry.com, has the benefit of an anti-tarnish coating to prevent oxidation. Therefore, LOS will not work well on certain brands unless the coating is removed.
If you do discover a brand of silver-plated wire that does not have a special coating, LOS will work to produce the patina you desire. Please be aware that most silver, or other metal plating, is rather thin. While you are finishing the patina process, a tumbler, fine sand paper, or steel wool can easily remove the metal plating, usually producing undesirable results (in other words, a mess!). I suggest experimenting with a few small pieces of each wire you are working with, to see if you are happy with the results. Remember to record your steps so that you can repeat them when you come up with a process you would like to repeat or improve on.
Answer contributed by Dale "Cougar" Armstrong