Promethium equipment (tier 10) is the second strongest melee equipment found in Daemonheim, behind Primal. The armour requires 90 defence to wear and the weapons need 90 attack or strength, depending on the weapon. It is the strongest smithable melee equipment.
Like gorgonite equipment, Promethium equipment cannot be found in the starting room. It can be dropped by monsters wielding promethium or primal equipment (as primal equipment is only dropped by bosses). Some bosses can also drop promethium equipment upon death.
To smith all pieces of promethium equipment, a Smithing level of 99 is required. If creating from scratch, you will also need a Mining level of 90.
Promethium, in real life, is a lanthanide-class element with an atomic number of 61 on the periodic table. This element's most stable isotope has a half-life of about 18 years. Promethium is rarely found in nature and cannot be made into alloys because of its rarity and properties, In addition to this, it emits beta radiation and would cause harm to those who are exposed.