Dvergar Soul Forges.

The Venerable Ancestors of the Dwarin laid down in the annuals of stone long ago that the use of forcibly binding souls in the great forges was strictly forbidden. Those who would tread this odious path would be driven mad by the souls they had forcibly stolen from the living to fashion more and more insidious creations. That this sickness that would consume you, until a smith found their own soul woven into their own masterwork. These Soul forges the Dwarin ancestor stoically warned of in their teachings would become the very life blood of Dvergar industry. Rejecting the teachings of the Dwarin ancestors whose own idleness had led to the collapse for their peoples once mighty Empire. Instead they turned to the more insidious deities of the deeps. Harking to themselves as tamers of the forbidden flame or Vulkans legacy.
Much about Dvergar industry and forging revolves around this illusive concept. Dvergar forge masters keep its practice a closely guarded secret. Requiring dragons fire, to bestow the raw elemental power that would aid them in the deepest parts of the world. The Dwarin repress all knowledge of it, reiterating the Ancestors teachings that the use of souls in forging and enchantment, was strictly forbidden and punishable by breaking the smiths hands beyond use. To master craftsmen amongst the Dwarin such a punishment is worse than death.
According to Dwarin tradition, it is Vulkan the forbidden one that discovered the abhorrent art. Taught it by the fiery Reishala mother of volcanos, whom had become infatuated with the mortal. Teaching him a number of forbidden arts not meant for mortal minds. When the Dwarin Ancestor gods were presented a number of glorious weapons and sets armours finer than anything any other blacksmith could produce, they asked Vulkan for his secret. When he told them, the ancestor gods were enraged. The Dwarin were ordered to destroy Vulkans workshop, dismantle the forges and would cursing him and any Dwarf who would dare attempt to recreate and use a soul forge. Banishing Vulkan and exiling him and branding him the Forbidden one. However, despite their best efforts the practice would continue to endure long after the fall of the empire.