A tiara is an item that can be created at a furnace from a silver bar along with a tiara mould and level 23 Crafting, granting 52.5 Crafting experience.
They are a purely cosmetic head slot item, though they can be turned into a talisman tiara, used in the Runecraft skill, acting as an equipable talisman (head slot), saving an inventory space over a normal talisman. It also allows the player to enter a particular runic altar by left-clicking on the corresponding mysterious ruins, saving time.
To create a talisman tiara, the player must have a tiara and the corresponding talisman in their inventory, and use the talisman or tiara on the altar of that particular rune. For example, a player who wishes to create an air tiara must enter the Air Altar ruins, and use the tiara on the altar with an air talisman in their inventory. The talisman itself is lost in the process.