Dragon Cleansing
Dragon Cleansing is the word Obellius Kalaar uses for what he does to a captured dragon: he draws something out of it, bottles it, and raises the emptied beast as a soldier. The word is his own. Nobody else in Eslura uses it without flinching.[1]
Where it is done
Dragons return to the core of a snowbound mountain, a cavern that Barnaby Britto guesses is about the size of the whole city of Ovallia, with a gurgling magma pool at its floor and gas geysers bursting off it. The way in is a mouth high on the mountainside, marked by a chipped wooden dragon sign and half buried in snowdrift, and three paths run down from it into the rock. The mountain is Alakyer, Eslura's highest peak, and its core is where dragons hatch.[2][3]
Two Nelazgian goons in obsidian armour were keeping three grown dragons there in cages when Barnaby, Alpin Loomin and Piercio looked down on the floor of the core from a ledge several storeys up.[3]
How it is done
Obellius walks along the cages telling the dragons they have been chosen to join their new king's army and what a great honour it is. He reaches a hand through the bars and lays it on the beast's snout. A black aura pulses around his fingertips, creeps onto the dragon and closes over its whole body in a glow, and the dragon drops where it stands.[1]
He then lifts his cloak. On the belt beneath it hang glass bottles, several already full of black swirling gas held in by corks. He takes an empty one, uncorks it, disperses the black aura into it and seals it. Then he tells the beast to rise. The first command does nothing; the second, spoken deeper and louder with his hand back on the snout, opens its eyes as two black spheres absent of the life and fire they once had, and it walks to his side. He worked through three dragons in a row without difficulty and left the core with them flapping behind him.[1]
The belt of corked bottles is the detail Barnaby recognises. Demise wore the same arrangement, and his bottles held the souls he took from living beings to add onto his own lifespan. Barnaby also recognises the blacked-out eyes.[1]
The cleansed dragons
The narration calls them Shadow Dragons. Barnaby, Alpin and Piercio cannot agree on a name, trying "A Shadow Reaper Dragon?" and "A Dragon Reaper?" and getting no further than that they are not good. Alpin's conclusion is that Obellius has found a way to use his powers to turn not only people into Reapers but dragons, and that there is no telling where he stops.[1]
Obellius left a standing order with his goons: any dragon that makes its way back to the core is to be captured and brought to him for cleansing. Piercio thought this was probably why a mother dragon had left the core with her clutch of eggs.[1]
Unexplained
The books show the act and refuse to explain it. What the black gas in the bottles is, whether it is a soul in the sense that Demise's bottles held souls, what Obellius does with the sealed bottles, and whether a cleansed dragon can be brought back are all left open. Piercio says plainly that he does not know what they are being turned into and is not sure he wants to know more.[1]