Sapphire.
The closest thing to permanence we know.
Single‑crystal sapphire is the same material that survives geological time. Ours is grown by the Kyropoulos method in Switzerland, by a family business operating since 1947, a slow process measured in weeks per ingot.
Hardness 9 on the Mohs scale, second only to diamond. It resists scratching, fading, chemical degradation and fire. The thinnest plate of corundum will outlast almost everything else humans choose to make.