In the past, If an orc that knew how to do a special royal fighting technique, they would give a perfect skull gem to their family priest first.
Perfect skull gems were just as important as top-quality magic gems to human wizards.
Most large magic circles were solely operated on perfect skull gems.
Only one perfect skull gem would be formed in the different death ground, or man made death ground of the orc empire.
Death grounds were made with large amounts of dead bodies, and they needed to be protected. Those pecker orcs in the orc empire were basically born to become an endless supply of dead bodies as long as they had enough food.
Despite that, most death grounds could form some normal skulls with lumps of death qi. You could get some higher quality ones if you were lucky, but perfect skull gems were still extremely rare. That was why most giant magic circle in the orc empire were empty.