Blank Rune

Blank Rune is a single use item that is meant to be used in conjunction with Mark, Portal, and Runebook.

Usage & Restrictions

 * In order to mark a Blank Rune, you must cast Mark, and target it from your inventory. This will create a Teleportation Rune marked with the caster's current location.
 * A marked rune cannot be re-marked.
 * You cannot Mark a rune while in a Dungeon, in a player's, on a player's property, or around the swap area of the Black Forest.

Source
Blank Runes can be bought for from the general stores in the following towns:
 * Valus
 * Eldeir Village
 * Pyros Landing
 * Oasis
 * Black Forest outpost
 * Helm