It is considered by Maester Yandel the best source for information on Qarth and the foremost work on the lands around the Jade Sea. In the Jade Compendium it is written that Azor Ahai's sword Lightbringer glows and is warm to the touch.
A Feast for Crows
The Jade Compendium is one of the stack of books that Samwell Tarly brings up from the library beneath Castle Black, along with Dragonkin, which Maester Aemon had commanded him to find. Making his way toward the armory Sam drops both books as he goes to catch Gilly by the arm. The Jade Compendium is undamaged but a few pages of Dragonkin are muddied.
A Dance with Dragons
Jon Snow tells Clydas that he looked at the book Maester Aemon left him. When Clydas expresses amazement at Azor Ahai's legendary heat-producing sword, Lightbringer, Jon states that Stannis Baratheon's sword is cold to the touch.
Aemon: Lord Snow, I left a book for you in my chambers. The Jade Compendium, it was written by the Volantene adventurer Colloquo Votar, who travelled to the east and visited all the lands of the Jade Sea. There is a passage you may find of interest. I've told Clydas to mark it for you.
Jon: I'll be sure to read it.Aemon: Knowledge is a weapon, Jon. Arm yourself well before you ride forth to battle.
The pages told of Azor Ahai. Lightbringer was his sword. Tempered with his wife's blood if Votar can be believed. Thereafter Lightbringer was never cold to the touch, but warm as Nissa Nissa had been warm. In battle the blade burned fiery hot. Once Azor Ahai fought a monster. When he thrust the sword through the belly of the beast, its blood began to boil. Smoke and steam poured from its mouth, its eyes melted and dribbled down its cheeks, and its body burst into flame.