Qyburn examines the effects of greyscale, the attempts to find a cure and the perception of those who suffer from it.
Qyburn: Few afflictions are more feared than greyscale, and far past the point of reason.
A legend calls it "Prince Garin's curse," after an ancient eastern prince whom the Valyrians hung in a cage and forced to watch the immolation of his city and people.
As his city burned under dragonflame, this prince called on his god for vengeance, and a thick fog of foul humors rose from the Rhoyne to smother the Valyrians with greyscale.
But if diseases could be called down by the vengeful, we would have no health in the world.
More likely the disease predates the Valyrians entirely, confined to some remote region of Essos, and only spread throughout the world once the Valyrians linked the continent with roads and dragons.
The disease begins as a rash. The afflicted flesh stiffens, calcifies, and cracks, and assumes the disease's nominal hue. Victims are graciously spared pain, as the disease dulls sensation in the infected limbs.
But the disease is insidious and slowly it creeps over the skin and into the organs. Once the infection reaches the brain, feral madness replaces humanity and the transformation to a stone man is complete.
There is no consensus on treatment. Some maesters advocate mustard poultices, vinegar rinses, and scalding hot baths. Others claim only three cures: ax, sword, and cleaver.
Hacking off afflicted parts does sometimes stop the spread of the disease, but not always.
Many a man has sacrificed an arm or foot only to find the other going grey.
Those who have been miraculously cured of greyscale are few and usually were subjected to so many treatments that isolating the responsible cure is impossible.
Besides, few maesters, priests, or healers have the courage for such experiments as would prove a cure.
Greyscale is highly contagious, being known to spread from even the slightest contact with an infected person.
Hence the current occupation of Valyria by the stone men, exiled from their homelands at the first sign of the disease. What they do with their final months or even years, for greyscale is a slow killer, no one knows.
No one wants to find out.
The map of Essos that appears in a book Qyburn is reading continues to depict the Jade Sea as extending north from Qarth. When George R.R. Martin provided the TV series with a larger map of Essos during Season 2, it was an early draft version. Later, however, he heavily revised the world map with the subsequent release of The Lands of Ice and Fire, establishing that in the book continuity, the Jade Sea extends south from the same latitude as Qarth. The TV series world maps were never updated to take these changes into account (it's possible they cannot, due to various copyright issues). Because Yi Ti is described as being on the north shore of the Jade Sea, this is makes the rather large difference of Yi Ti being at the same latitude as Pentos in the TV version maps, and at the same latitude as Volantis in the book version maps.