Forge Sun Silver

At the time of Arrival, 4 out of six deities chose to create a people using their magics and powers. 2 of them, the twins Elios and Lyra, chose to create weapons with the souls of some of the most powerful people from their homeworlds to imbue them. The weapons would then bond to people of 4 Corners who were deemed worthy and a match to the weapon. And, thus, Elios' Scarlet Knights and Lyra's Shadows were born.
Elios' weapons were created out of a material that was rare and beautiful known as Forge Sun Silver. It was the same material his gate was created out of when he arrived onto the world of 4 Corners, and the first stone placed in the Caldera that gives the island of the Forge its name still glows bright hot to this day. It is said that the metal naturally glows bright white, hot as the surface as the sun, and the weapons are only tempered and cool to the touch to the proper bearer of the sword. Any soul who tries to touch it that is not meant to bond with the weapon will be burnt instantly, and a mark of the weapon's unique pommel left permanently on the hand as a reminder to never try again. 
It is important to note that the metal itself, is not so hot and volatile, but combining the magics and the soul within keep the metal of the weapons hot as the sun to touch. 
The Caldera of the Forge is also incredibly unique. The Keystone provides all the warmth and base heat that lights the rest of the hearth's fuel. It all burns hotter than a normal fire, and it takes trainees at the Forge (both Scarlet Knight hopefuls and others looking to learn the trade of smithing in a Forge Sun hearth and how to work with the silver) years of apprenticeship after regular smith training to learn how to work with it properly. One of the signs of a master is the ability to create chainmail out of the metal. This takes time, patience, and a considerable amount of skill to properly temper the metal without it becoming brittle. The metal in this format is the only substance in existence that can insulate a nonbearer's hands from one of the 15 Sacred weapons, allowing the weapon to be moved and transported back to the Forge if and when a Scarlet Knight falls.  
Forge Sun Silver is only obtainable in the areas of the desert where the Twin God's gates were created and was mined all the way up until the Fall of Crossroads. (Though the actual location of both Lyra's and Elios' gates have long been a mystery and a search that no soul has been successful in finding since the time of the Fall of Fezzeret) Since Narne's take over of the region, the warlord has any and all control over the mining operations. It is speculated that the Forge Sun Silver mines were one of her primary reasons for destroying Crossroads and taking over its territory, however no soul has ever lived to return and deliver such intel.