Amulet of Shield

This is a plain silver amulet on a silver chain with fine carvings that hold the enchantment. This item lets the wearer cast shield once per short rest with a max of 4 charges. Charges can be regained (1d4) per long rest. If all 4 charges are used before it can recharge roll a (d100/%) on a 100 or a 000 the item loses is enchantment and becomes a mundane amulet   

Notes: Amulet of Shield Requires Attunement by a Caster