The strength and density of the High Metals limits how they can be used.  Argentium is twice as dense as Aurium, and Adamatium twice as dense as Argentium. The melting point of Gold is fairly low, that of Adamantium almost impossibly high. Gold is so soft and easy to work that it is useless for making weapons, whereas Adamantium is too heavy and hard to work to be made into chain mail. Aurium is so ductile that it can be spun into thread and mixed with threads to form a kind of metallic cloth.

There are two possibly alloys of the High Metals, those these are incredibly difficult to create and rarely seen. They are Electrum (Aurium and Mithril) and Adagentium (Adamantium and Mithril, also called Adamantril).  The creation of the alloys itself requires the work of Master Smith in a demanding act of ArtCraft. These alloys are useful in that they display the best traits of their parent metals and do not activate the sensitivity of Faeries. Thus Seelie Knights can use weapons with near the strength and sharpness of Adamantium, via Adamanthril, without the deep revulsion that contact with actual Iron would cause.

As to the Low Metals, as they are called by the few who even know of their existance, Viridium, Irisium, Azurium and Cinnibrium, each has certain problems that make them impractical. First is rarity - any of them are worth ten times their weight in diamonds. Viridium is a green metal, softer even than Aurium and useless for any kind of physical application. Irisium, though beautiful beyond compare, covered with shifting rainbow auras, is harder to work than Adamantium and is found only in one area of the Burning Desert. Azurium is a royal blue metal which is found only in the deepest Waters and begins to corrode immediately on exposure to air. Cinnibrium, though as workable as Argentium, reacts with blood, corroding rapidly. There are rumored to be other Low Metals, though they must be rare beyond hope of collection. These Low Metals will alloy with each other, but not with the HighMetals. Their only real use in certain ArtCrafts (and other Magics), and as Jewelery.

There is another option in the form of Vitredur, which a form of magically shaped diamond. It is incredibly expensive, but lighter and stronger than Adamatium, though just as difficult to work. For the most part, it is used to make swords, shields and armor plates to be attached to suits of Mithril mail.

There is also Weirwood. Weirwood is easily enchanted and can be rendered almost as durable as Mithril, and is much lighter. Weirwood makes up most of the everyday utensils  used throughout Worldstree. Though chainmail of weirwood is impractical, plates of weirwood over mithril chain and armor made of weirwood slates and overlapping scales is quite common. Also, Weirwood trees can be infused with the HighMetals, yeilding GoldWood, SilverWood and IronWood. The weirwood then takes on some of the properties of the High Metals, including the damaging effects.

Moridur is formed from the petrified bodies of dead Faeries, and it's use is outlawed in civil Lands.