The Mask of Metal Beak was a metal mask made to protect and conceal Kludd's battle-torn face when he became the High Tyto. Often, replacements have to be made, when the mask was beyond repair. It is made of mu metal to protect from the flecks the Pure Ones use.
Kludd wore the mask in the battle at the Devil's Triangle. Soren ripped off a great piece of the mask, revealing Metal Beak's true identity. The mask then began melting when Soren lashed a burning branch at it, forcing Kludd to retreat.
Kludd finally found a pool and plunged into it, cooling down the melting metal. After recovering, Metal Beak had the Pure Ones force the Rogue Smith of Silverveil to make a new mask that's to be made of mu metal, so it'll be invulnerable to flecks and fire.
After Kludd died in the Battle of Ice and Fire, his mask and battle claws were collected by his mate, Nyra. When Kludd appeared to Nyroc as a scroom, he was portrayed as the mask that he wears. Nyroc eventually disowned Kludd, said that he was just a mask, and charged at the mask, shattering it and putting Kludd in hagsmire.
Nyra gathered the remnants of Kludd's original mask and had a Rogue Smith forge a new one from those fragments. She wore it in the battle at the Middle Kingdom. The mask was left behind on some dead owls. It was recovered later by her.
As supreme leader of the Pure Ones, Surtr wore a helmet which was much more unique than the ones worn by his soldiers. During the battle of the Ice Claws, he fought Leize of Kiel, who slashed off a large part of his beak. Afterwards, Surtr added a new part to the helmet to cover his ruined beak.