The strong runecrafting urn (r) is created by using a pure essence on a strong runecrafting urn (nr). It can be used to collect rune remnants while crafting runes (including Runespan) that require level 77 Runecrafting or lower. Once it starts to get filled, it becomes a Strong runecrafting urn. You get 1,000 runecrafting experience when you teleport the urn to Ernie.