We are often asked the question: "What are those little black squares that came with my string??"
Those little black squares are anti-tarnish strips put in the envelopes of strings wound in sterling silver to avoid tarnish. Sterling tarnishes, turning black-ish in color, and cosmetically looks bad. The anti-tarnish strips react to hydrogen sulfide and other tarnish-causing gases to neutralize them. If the silver string tarnishes it is still perfectly fine, but these little squares help prevent tarnish.