Tempered in Darkness

The beasts of Quel'Thalas produce leather of unparalleled quality, but the Void has been doing something strange to it. Normally, we harden leather by heating it under specific conditions. But the darkness clinging to these hides seems to be tempering the leather on its own. I have no idea how this is possible, but we can make use of it. Bring me as much as you can gather. We have an army to supply.