Faerstone

Faerstone is a rust-colored metallic substance with the unique ability to meld metals to sapient minds. When properly cut and traced into larger pieces of iron or bronze and laced through a subject's skin, the metal begin to respond to the subject's mental commands, though full symbiosis can take months or years. A trained Artificer can use faerstone as a temporary storage medium for Eleth and can form Biofaerics through skilled smithwork.   Faerstone is produced entirely by hand by large Artificer guilds, as minor deviations in its properties make the stone useless. The stone itself is an amalgam of iron and gold, forged in the high pressures and heat of a volcanic rift, though the exact metallurgical formula is a closely guarded secret.