The plain runecrafting urn (r) is created by using a pure essence on a plain runecrafting urn (nr). It can be used to collect rune remnants while crafting runes (including Runespan) that require level 54 Runecrafting or lower. Once it starts to get filled, it becomes a plain runecrafting urn. You get 700 runecrafting experience when you teleport the urn to Ernie.