Etherium

Etherium is a magical aether-infused alloy found on Esper. Another name for the same substance is filigree.

Description
According to the myth, etherium was created by the sphinx Crucius, and since then most of Esper's inhabitants have parts of their body replaced by etherium. The body's functions are kept up through a series of complex enchantments. The stocks of etherium are measured in rods. Ultimately the Ethersworn are planning to fuse every living being with this metal. The greatest masters of the craft abandon tools all-together, shaping the metal with hand and mind alone.

The inhabitants of Esper believed that all life and every physical form was incomplete without some connection to the Aether via filigree or etherium fusing. As they could not create new etherium themselves, their supplies of it were very limited, so mages began to use more subtle fusions with lower-class life forms.

Origin
It is unknown how Crucius made the alloy; even Sharuum could only show how to thin existing etherium. The Seekers of Carmot believed that the substance was made from the materials known as sangrite and carmot. They possessed the Codex Etherium, which supposedly reveals the location of both; however, it was revealed by Tezzeret that the Codex was a fraud.

Sangrite, a magical bloodstone that stores the lifeforce of creatures that have died, was revealed to be the petrified blood of a dragon who dies in battle and can only be found on Jund, thus explaining why the Esperites could not craft new etherium. As Crucius was himself a planeswalker, he could obtain sangrite from Jund.

Mining rights
Tezzeret and Nicol Bolas fought over mining rights on an unnamed plane, where Tezzeret claimed the ores needed to create etherium came from. It is unclear if this was on Esper, Jund, or some other plane.

After the Conflux
After the Conflux, the Seekers sent emissaries into the other shards, seeking carmot at any cost. It was revealed by Tezzeret that he was the Carmot, but it is unknown whether he meant only himself, all Esperites, or humans in general.

Later, the human Breya was the first to create Etherium from Carmot harvested from Jund. To commemorate this, she replaced most of her body with self-crafted etherium.

Etherium artifacts
Notable items made of etherium are the "Filigree Texts" and Tezzeret's Infinity Globes.