It is unlikely there is a being alive who knows by what force this cloak was crafted. The very essence of it soaks up magic, both incoming and from the wearer. How one would go about crafting such an item with magical means is a mystery many have tried to solve. Some believe only a god could embed energy so opposite to magic in an item like this. that would indeed explain why they are so rare. Many powerful mages in times past have attempted to craft such items, only managing at best to create a very inferiour replica or more often destroying themselves when the source of antimagic sucks them in like a vortex. Most living experts have now resigned themselve to the fact we shall never know for sure.