Necklace of the Diamond’s Edge

Wondrous item, rare (requires attunement)

This necklace is decorated with twelve diamonds up to an inch long and a thirteenth larger diamond holding it together. As an action, you can detach one of the smaller diamonds and hold it to a melee weapon. The diamond disappears, merging with the weapon and infusing it with its power. The weapon becomes magical for one hour, gaining a +1 to attack and damage. While infused, attacks with this weapon deal 1d4 extra damage. These effects last for 1 hour.

The diamonds do not reappear on the necklace.

Once they are all gone, the thirteenth diamond turns the necklace into an item of protection, granting a +1 to your Armor Class while worn.