Aetherform Weapons

Many of the legends of old are born from Aetherform Weapons. The Sword of the Five dragons. Jon of Harlik's Lance. Lady Anterllis' famously keen stilleto. 
The description of their sharpness and the similarity of their depiction to Old Empire Aetherform Weapons as well as, ironically, the variance in descriptions of specific items, all paint them as Aetherform. 
Some of these examples, should they still exist within the modern age, are likely some of the oldest examples of Aether manipulating devices left in the world. 

-The Sage of Red Lillies, Codex Imperial

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With blades that seem made from light and honed to an edge far sharper than a razor can manage, Aetherform Weapons are a wonder of technology and Aether manipulation. 
Nothing we can make in the modern world can match the weapons ability to condense magic, nor it's precise control. Most certainly not in so small a package as the hilt of a sword or haft of a spear. 
The only way to protet against one, as long as one skill in swordplay is matching an opponent, is to have an Aetherform Weapon in your possession. Otherwise, that blade of pure magic will cut through any mundane blade or armor you may hold like it wasn't there in the first place. Even enchanted weapons, which are more durable than their mundane counterparts, only provide passing resistance to an Aetherform blade. A few strikes are all one could parry before it to has it's blade severed like all the rest.
The only thing, other than another Aetherform weapon, that can resist the impossible edge these weapons have is a weapon or defense crafted from Blackstone. The two opposing properties, purely magical and magically absorbant and retentive, result in each being resistant to the damages of the other. A cancelation of their inherent benefits.