User blog comment:Sorairo/Aura, Dust, and the RWBY Panel/@comment-11188061-20130823055451/@comment-15108745-20130823064338

Well, here's what I know about silver:
 * It's frequently associated with the supernatural. Usually as some sort of purifying device.
 * This probably comes from the fact that it's a very good antibacterial. So silver is associated with purifying. So it's kinda like innocence in that it's associated with purity...
 * Silver is associated with the moon. In fact the word luna was actually used in alchemy to represent the metal silver.