Silver tarnishes because it reacts to the sulfur/hydrogen sulfur in the air. I assume that if the necklace is tarnishing so quickly it likely means that there is an unusual amount of sulfur or hydrogen sulfur in the air or, more likely, the reactant in the silver that causes ir to tarnish is found in an unusually high amount in that particular piece of jewellery.
Silver will tarnish. The black is silver oxide. It will polish away with good silver polish. Or mix baking soda and water, place a bit of aluminum foil in the water, put the silver in and let it soak for a few hours.
The duration of The Affair of the Necklace is 1.97 hours.
Tarnishing usually occurs on metal surfaces when they react with substances like air, water, or chemicals. This reaction causes a darkening or discoloration of the metal, resulting in a dull appearance. It can be prevented by storing metals properly and keeping them away from harsh environments or conditions.
The duration of The Silver Fez is 1.38 hours.
The duration of The Silver Fleet is 1.47 hours.
The duration of Operace Silver A is 2.48 hours.
The duration of Silver Case is 1.43 hours.
The duration of Silver Hawk is 1.65 hours.
The duration of Silver Saddle is 1.67 hours.
The duration of The Silver Cliff is 1.38 hours.
The duration of Silver Stallion is 2.05 hours.
The duration of Silver Queen is 1.33 hours.