This delicate marble ring was created by the Ironcrag dwarves who battle the ghouls and vampires of the duchies in the Grisal Marches. When you slip the band onto the finger of a corpse, it protects the body from decay, and the corpse cannot become undead as long as the ring remains on its finger.
Days the corpse spends wearing the ring don’t count as days spent dead, effectively extending the time limit on spells such as raise dead.