Celestial Bronze

Celestial Bronze is a powerful metal of magical nature made mostly by the Cyclopes' forges and Hephaestus. It is harmful only to gods, demigods, titans and monsters. Celestial bronze weapons will not harm mortals, as they are not as important as immortals and monsters. Celestial bronze is mined from Mount Olympus, then forged by the Cyclopes, tempered in the heart of Mount Etna and cooled in the River Lethe. Demigods and gods favor celestial bronze weapons because they are able to wound immortals (example of when Percy wounded Ares in the heel), and kill monsters and half-bloods, however it will pass through mortals like an illusion (take for instance, when Percy swung Riptide at Rachel Dare, it passed through her as if she was an illusion), whereas mundane iron or steel weapons bounce off of most magical beings uselessly. It's debatable how strong Celestial Bronze is as Percy Jackson managed to cut through a steel car door as if it was made of plastic wrap but Geryon managed to deflect the sword using nothing more than a pair of steel tongs, so its safe to consider that Celestial Bronze is somewhat greater than steel. Demigods, being half-god, can be harmed and even killed by celestial bronze. Celestial bronze is also used in god and demigod armor.

Notable Use

 * Riptide is Percy's Celestial bronze sword.
 * Annabeth has a Celestial bronze knife, given to her by Luke Castellan.
 * Zeus' Lightning Bolt has a cylinder made up of high-grade Celestial bronze.
 * Professor Chase, Annabeth's father, melted down the weapons that she left in her room the last time she ran away, and forged them into machine gun bullets for his Sopwith Camel bi-plane, which he used to kill monsters, buying time for Percy and his friends to escape during The Titan's Curse.
 * Luke's sword, Backbiter is half Celestial bronze and half steel. It is the sword version of Kronos' scythe.
 * Thalia's spear is made of Celestial Bronze and is one of Thalia's main weapons before she became a Hunter of Artemis.
 * Katoptris is Piper McLean's Celestial bronze dagger.

Trivia

 * Stygian iron is very similar to Celestial bronze, but can only be used by Underworld deities and their children because it is made from the River Styx. Nico di Angelo has a Stygian iron sword.
 * Celestial bronze can be melted at high temperatures.
 * Imperial Gold is very similar to Celestial bronze, but is mostly used by the Roman Demigods