Full: Hold Glaive's ashes for up to 30...54...60 seconds. While you hold her ashes, all Ritualist skills have 20% armor penetration. When you drop her ashes, all foes in the area are struck for 15...71...85 lightning damage.
Concise: (30...54...60 seconds.) Your Ritualist skills have 20% armor penetration. Drop effect: deals 15...71...85 lightning damage to all foes in the area.
The armor penetration also applies to damage done by dropping the ashes.
When used with Spirit Rift, the armor penetration will only be gained if you are holding the Ashes when the damage triggers; the spell does not check whether or not you were holding them when the spell was cast.
Anomaly! When dropped, the dropped item is listed as a 'Destructive Was Glaive', rather than 'Ashes of Destructive Glaive'.