Ritual: Yog's Protection

Description
A spiritual residue left on religious altars
 *  is a defensive shield that projects a sphere centered on the Altar about 10 foundations in every direction.
 * It is crafted within the altar with the materials below and lasts for 36 hours.
 * The altar must be Tier 3 and contain an archpriest or a named Priest Thrall for the recipe to appear. Neither are consumed in the process.
 * Splash damage from explosive arrows and gas mixed will penetrate the shield.

Source
1 craftable with a T3, T4, T4 (purge) Priest thrall in the crafting station